Inno Setup Could not call proc error?

So I'm trying to build an installer for a source port called DXX-Rebirth. I compiled it, and when I run I get a "could not call proc" error right after the language select dialog. The error points to the function Descent. Here is my .iss file:

; Script generated by the Inno Setup Script Wizard.
; SEE THE DOCUMENTATION FOR DETAILS ON CREATING INNO SETUP SCRIPT FILES!

#define MyAppName "DXX-Rebirth"
#define MyAppName1 "D1X-Rebirth"
#define MyAppName2 "D2X-Rebirth"
#define MyAppVersion "0.57.0"
#define MyAppURL "http://www.dxx-rebirth.com/"
#define MyAppExeName "d1x-rebirth.exe"
#define MyAppExeName2 "d2x-rebirth.exe"

[Setup]
; NOTE: The value of AppId uniquely identifies this application.
; Do not use the same AppId value in installers for other applications.
; (To generate a new GUID, click Tools | Generate GUID inside the IDE.)
AppId={{DF665ED8-D2A7-490A-805F-6677EFFBAB40}
AppName={#MyAppName}
AppVersion={#MyAppVersion}
;AppVerName={#MyAppName} {#MyAppVersion}
AppPublisherURL={#MyAppURL}
AppSupportURL={#MyAppURL}
AppUpdatesURL={#MyAppURL}
DefaultDirName={pf}\{#MyAppName}
DefaultGroupName={#MyAppName}
OutputBaseFilename=Setup
Compression=lzma
SolidCompression=yes

[Languages]
Name: "english"; MessagesFile: "compiler:Default.isl"
Name: "german"; MessagesFile: "compiler:Languages\German.isl"

[Tasks]
Name: "desktopicon"; Description: "{cm:CreateDesktopIcon}"; GroupDescription: "{cm:AdditionalIcons}"; Flags: unchecked
Name: "quicklaunchicon"; Description: "{cm:CreateQuickLaunchIcon}"; GroupDescription: "{cm:AdditionalIcons}"; Flags: unchecked

[Types]
Name: "install"; Description: "DXX-Rebirth"; Flags: iscustom

[Components]
Name: "d1x"; Description: "D1X"; Types: install
Name: "d2x"; Description: "D2X"; Types: install

[Files]
;D1X Files
Source: "C:\Documents and Settings\Owner\Desktop\Downloads\d1x-rebirth_v0.57-win\d1x-rebirth_v0.57-win\d1x-rebirth.exe"; DestDir: "{app}\D1X-Rebirth"; Components: d1x; Flags: ignoreversion
Source: "C:\Documents and Settings\Owner\Desktop\Downloads\d1x-rebirth_v0.57-win\d1x-rebirth_v0.57-win\*"; DestDir: "{app}\D1X-Rebirth"; Excludes: "C:\Documents and Settings\Owner\Desktop\Downloads\d1x-rebirth_v0.57-win\d1x-rebirth_v0.57-win\Missions,C:\Documents and Settings\Owner\Desktop\Downloads\d1x-rebirth_v0.57-win\d1x-rebirth_v0.57-win\Players,C:\Documents and Settings\Owner\Desktop\Downloads\d1x-rebirth_v0.57-win\d1x-rebirth_v0.57-win\Demos,C:\Documents and Settings\Owner\Desktop\Downloads\d1x-rebirth_v0.57-win\d1x-rebirth_v0.57-win\Screenchots"; Components: d1x; Flags: ignoreversion recursesubdirs createallsubdirs
Source: "C:\Documents and Settings\Owner\Desktop\Downloads\d1x-rebirth_v0.57-win\d1x-rebirth_v0.57-win\Missions"; DestDir: "{app}\D1X-Rebirth"; Components: d1x; Flags: ignoreversion recursesubdirs createallsubdirs onlyifdoesntexist
Source: "C:\Documents and Settings\Owner\Desktop\Downloads\d1x-rebirth_v0.57-win\d1x-rebirth_v0.57-win\Players"; DestDir: "{app}\D1X-Rebirth"; Components: d1x; Flags: ignoreversion recursesubdirs createallsubdirs onlyifdoesntexist
Source: "C:\Documents and Settings\Owner\Desktop\Downloads\d1x-rebirth_v0.57-win\d1x-rebirth_v0.57-win\Demos"; DestDir: "{app}\D1X-Rebirth"; Components: d1x; Flags: ignoreversion recursesubdirs createallsubdirs onlyifdoesntexist
Source: "C:\Documents and Settings\Owner\Desktop\Downloads\d1x-rebirth_v0.57-win\d1x-rebirth_v0.57-win\Screenshots"; DestDir: "{app}\D1X-Rebirth"; Components: d1x; Flags: ignoreversion recursesubdirs createallsubdirs onlyifdoesntexist
;D1 Main Files
Source: "{code:Descent}\descent.hog"; DestDir: "{app}\D1X-Rebirth"; Components: "d1x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: 开发者_如何学编程"{code:Descent}\descent.pig"; DestDir: "{app}\D1X-Rebirth"; Components: "d1x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
;D1 Missions
Source: "{code:Descent}\*.hog"; DestDir: "{app}\D1X-Rebirth\Missions"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:Descent}\*.msn"; DestDir: "{app}\D1X-Rebirth\Missions"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:Descent}\*.rdl"; DestDir: "{app}\D1X-Rebirth\Missions"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:Descent}\Missions\*"; DestDir: "{app}\D1X-Rebirth\Missions"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
;D1 Players
Source: "{code:Descent}\*.eff:"; DestDir: "{app}\D1X-Rebirth\Players"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:Descent}\*.plr:"; DestDir: "{app}\D1X-Rebirth\Players"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:Descent}\*.plx:"; DestDir: "{app}\D1X-Rebirth\Players"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:Descent}\*.ngp:"; DestDir: "{app}\D1X-Rebirth\Players"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:Descent}\*.sg*:"; DestDir: "{app}\D1X-Rebirth\Players"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:Descent}\*.mg*:"; DestDir: "{app}\D1X-Rebirth\Players"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:Descent}\Players\*.eff:"; DestDir: "{app}\D1X-Rebirth\Players"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:Descent}\Players\*.plr:"; DestDir: "{app}\D1X-Rebirth\Players"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:Descent}\Players\*.plx:"; DestDir: "{app}\D1X-Rebirth\Players"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:Descent}\Players\*.ngp:"; DestDir: "{app}\D1X-Rebirth\Players"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:Descent}\Players\*.sg*:"; DestDir: "{app}\D1X-Rebirth\Players"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:Descent}\Players\*.mg*:"; DestDir: "{app}\D1X-Rebirth\Players"; Components: "d1x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
;D2X Files
Source: "C:\Documents and Settings\Owner\Desktop\Downloads\d2x-rebirth_v0.57-win\d2x-rebirth_v0.57-win\d2x-rebirth.exe"; DestDir: "{app}\D2X-Rebirth"; Components: d2x; Flags: ignoreversion
Source: "C:\Documents and Settings\Owner\Desktop\Downloads\d2x-rebirth_v0.57-win\d2x-rebirth_v0.57-win\*"; DestDir: "{app}\D2X-Rebirth"; Excludes: "C:\Documents and Settings\Owner\Desktop\Downloads\d2x-rebirth_v0.57-win\d2x-rebirth_v0.57-win\Missions,C:\Documents and Settings\Owner\Desktop\Downloads\d2x-rebirth_v0.57-win\d2x-rebirth_v0.57-win\Players,C:\Documents and Settings\Owner\Desktop\Downloads\d2x-rebirth_v0.57-win\d2x-rebirth_v0.57-win\Demos,C:\Documents and Settings\Owner\Desktop\Downloads\d2x-rebirth_v0.57-win\d2x-rebirth_v0.57-win\Screenshots"; Components: d2x; Flags: ignoreversion recursesubdirs createallsubdirs
Source: "C:\Documents and Settings\Owner\Desktop\Downloads\d2x-rebirth_v0.57-win\d2x-rebirth_v0.57-win\Missions"; DestDir: "{app}\D2X-Rebirth"; Components: d2x; Flags: ignoreversion recursesubdirs createallsubdirs onlyifdoesntexist
Source: "C:\Documents and Settings\Owner\Desktop\Downloads\d2x-rebirth_v0.57-win\d2x-rebirth_v0.57-win\Players"; DestDir: "{app}\D2X-Rebirth"; Components: d2x; Flags: ignoreversion recursesubdirs createallsubdirs onlyifdoesntexist
Source: "C:\Documents and Settings\Owner\Desktop\Downloads\d2x-rebirth_v0.57-win\d2x-rebirth_v0.57-win\Demos"; DestDir: "{app}\D2X-Rebirth"; Components: d2x; Flags: ignoreversion recursesubdirs createallsubdirs onlyifdoesntexist
Source: "C:\Documents and Settings\Owner\Desktop\Downloads\d2x-rebirth_v0.57-win\d2x-rebirth_v0.57-win\Screenshots"; DestDir: "{app}\D2X-Rebirth"; Components: d2x; Flags: ignoreversion recursesubdirs createallsubdirs onlyifdoesntexist
;D2 Main Files
Source: "{code:DescentTwo}\descent2.ham"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\descent2.hog"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\descent2.s11"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\descent2.s22"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\alien1.pig"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\alien2.pig"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\fire.pig"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\groupa.pig"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\ice.pig"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\water.pig"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\intro-h.mvl"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\intro-l.mvl"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\other-h.mvl"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\other-l.mvl"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\robots-h.mvl"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\robots-l.mvl"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
;Vertigo
Source: "{code:DescentTwo}\d2x-h.mvl"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\d2x-l.mvl"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\hoard.ham"; DestDir: "{app}\D2X-Rebirth"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\d2x.hog"; DestDir: "{app}\D2X-Rebirth\Missions"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\d2x.mn2"; DestDir: "{app}\D2X-Rebirth\Missions"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\Missions\d2x.hog"; DestDir: "{app}\D2X-Rebirth\Missions"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\Missions\d2x.mn2"; DestDir: "{app}\D2X-Rebirth\Missions"; Components: "d2x"; Check: not DontInstall; Flags: external skipifsourcedoesntexist
;D2 Missions
Source: "{code:DescentTwo}\*.hog"; DestDir: "{app}\D2X-Rebirth\Missions"; Components: "d2x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\*.mn2"; DestDir: "{app}\D2X-Rebirth\Missions"; Components: "d2x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\Missions\*"; DestDir: "{app}\D2X-Rebirth\Missions"; Components: "d2x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
;D2 Players
Source: "{code:DescentTwo}\*.eff:"; DestDir: "{app}\D2X-Rebirth\Players"; Components: "d2x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\*.plr:"; DestDir: "{app}\D2X-Rebirth\Players"; Components: "d2x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\*.plx:"; DestDir: "{app}\D2X-Rebirth\Players"; Components: "d2x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\*.ngp:"; DestDir: "{app}\D2X-Rebirth\Players"; Components: "d2x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\*.sg*:"; DestDir: "{app}\D2X-Rebirth\Players"; Components: "d2x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\*.mg*:"; DestDir: "{app}\D2X-Rebirth\Players"; Components: "d2x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\Players\*.eff:"; DestDir: "{app}\D2X-Rebirth\Players"; Components: "d2x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\Players\*.plr:"; DestDir: "{app}\D2X-Rebirth\Players"; Components: "d2x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\Players\*.plx:"; DestDir: "{app}\D2X-Rebirth\Players"; Components: "d2x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\Players\*.ngp:"; DestDir: "{app}\D2X-Rebirth\Players"; Components: "d2x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\Players\*.sg*:"; DestDir: "{app}\D2X-Rebirth\Players"; Components: "d2x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
Source: "{code:DescentTwo}\Players\*.mg*:"; DestDir: "{app}\D2X-Rebirth\Players"; Components: "d2x"; Check: InstallAll; Flags: external skipifsourcedoesntexist
; NOTE: Don't use "Flags: ignoreversion" on any shared system files

[Icons]
Name: "{group}\{#MyAppName1}"; Filename: "{app}\D1X-Rebirth\{#MyAppExeName}"
Name: "{group}\{#MyAppName2}"; Filename: "{app}\D2X-Rebirth\{#MyAppExeName2}"
Name: "{group}\{cm:UninstallProgram,{#MyAppName}}"; Filename: "{uninstallexe}"
Name: "{commondesktop}\{#MyAppName1}"; Filename: "{app}\D1X-Rebirth\{#MyAppExeName}"; Tasks: desktopicon
Name: "{commondesktop}\{#MyAppName2}"; Filename: "{app}\D2X-Rebirth\{#MyAppExeName2}"; Tasks: desktopicon
Name: "{userappdata}\Microsoft\Internet Explorer\Quick Launch\{#MyAppName1}"; Filename: "{app}\D1X-Rebirth\{#MyAppExeName}"; Tasks: quicklaunchicon
Name: "{userappdata}\Microsoft\Internet Explorer\Quick Launch\{#MyAppName2}"; Filename: "{app}\D2X-Rebirth\{#MyAppExeName2}"; Tasks: quicklaunchicon

[Run]
Filename: "{app}\D1X-Rebirth\{#MyAppExeName}"; Description: "{cm:LaunchProgram,{#StringChange(MyAppName1, "&", "&&")}}"; Flags: nowait postinstall skipifsilent unchecked
Filename: "{app}\D2X-Rebirth\{#MyAppExeName2}"; Description: "{cm:LaunchProgram,{#StringChange(MyAppName2, "&", "&&")}}"; Flags: nowait postinstall skipifsilent unchecked

[Code]
// global vars
var
  SampleDataPage: TInputOptionWizardPage;
  DataDirPage: TInputDirWizardPage;

// custom wizard page setup, for data dir.
procedure InitializeWizard;
begin
  { Taken from CodeDlg.iss example script }
  { Create custom pages to show during install }

  SampleDataPage := CreateInputOptionPage(wpSelectComponents,
    'Install Descent Data', '',
    'Would you like to copy the Descent game files to your DXX-Rebirth installation?',
    True, False);
  SampleDataPage.Add('Yes copy the game files, missions, players, and savegames.');
  SampleDataPage.Add('Yes, but just copy the game files.');
  SampleDataPage.Add('No, I'+chr(39)+'ll copy the game files myself later.');

  SampleDataPage.Values[0] := True;

  DataDirPage := CreateInputDirPage(SampleDataPage.ID,
  'Descent Data Directory', '',
  'Please select the location where the original Descent files are installed.',
  False, '');
  DataDirPage.Add('Descent location.');
  DataDirPage.Add('Decent 2 location.');

  DataDirPage.Values[0] := ExpandConstant('{pf}\GOG.com\Descent and Descent 2\Descent');
  DataDirPage.Values[1] := ExpandConstant('{pf}\GOG.com\Descent and Descent 2\Descent 2');

end;

function InstallAll(): Boolean;
begin
  { Return the value of the 'install' radiobutton }
  //MsgBox('InstallSampleData.', mbError, MB_OK);
  Result := SampleDataPage.Values[0];
end;

function Install(): Boolean;
begin
  { Return the value of the 'install' radiobutton }
  //MsgBox('InstallSampleData.', mbError, MB_OK);
  Result := SampleDataPage.Values[1];
end;

function DontInstall(): Boolean;
begin
  Result := SampleDataPage.Values[2];
end;

function Descent(Param: String): String;
begin
  { Return the selected DataDir }
  //MsgBox('GetDataDir.', mbError, MB_OK);
  Result := DataDirPage.Values[0];
end;

function DescentTwo(Param: String): string;
begin
  { Return the selected DataDir }
  //MsgBox('GetDataDir.', mbError, MB_OK);
  Result := DataDirPage.Values[1];
end;

Thanks in advance! :)

The problem is order of execution.

If you step through the code you will find that that the {code:Descent} lines are executed before the call to InitializeWizard And because of that DataDirPage is not created.

The good news is that the code is also evaluated on install.

Changing the code to this should make it work.

function Descent(Param: String): String;
begin
    if Assigned(DataDirPage) then
   result := DataDirPage.Values[0]
  else 
   result := '';
end;

function DescentTwo(Param: String): string;
begin
if Assigned(DataDirPage) then
   result := DataDirPage.Values[1]
  else 
   result := '';
end;