Debugging System.TypeLoadException

I'm trying to compile Boo on the mono-4.0 Nant profile and am getting the following error, which I'm having trouble debugging.

booi:

Invalid type Boo.Lang.Compiler.CompilerParameters for instance field Boo.Lang.Compiler.CompilerContext:_parameters
Missing method .ctor in assembly /Users/tristanz/Projects/boo/build/Boo.Lang.Compiler.dll, type System.Security.SecurityRulesAttribute
Can't find custom attr constructor image: /Users/tristanz/Projects/boo/build/Boo.Lang.Compiler.dll mtoken: 0x0a00097b

BUILD FAILED - 0 non-fatal error(s), 2 warning(s)

INTERNAL ERROR

System.TypeLoadException: Could not load type 'System.Security.SecurityRulesAttribute' from assembly 'Boo.Lang.Compiler'.
  at Boo.NAnt.BooTask.ExecuteTask () [0x00000] in <filename unknown>:0 
  at NAnt.Core.Task.Execute () [0x00000] in <filename unknown>:0

Any thought开发者_JAVA技巧s would be greatly appreciated.

The problem is that NAnt itself must run under 4. for the BooTask to correctly work, so mono --runtime=v4.0 is the fix.