unable to compile code after upgrade to .net 3.5

I am in Visual Studio 2008 env using c#, upgraded to .net 3.5 and now keep getting below compile error:

I have reset my dll references and add them back in but no help :( very frustrated.

Error 1 The type 'System.ComponentModel.IComponent' is defined in an assembly that is not referenced. You must add a reference to assembly 'System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'. C:\Documents and Settings\admin\Desktop\AccountActivation.aspx.cs 21 26 tissot4

My web.config file:

-->

-->

<add assembly="System.Web.Extensions.Design, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
<add assembly="System.Design, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"/>

    <!--><add assembly="System.Windows.Forms, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
    -->
  </assemblies>

section enables configuration of the security authentication mode used by ASP.NET to identify an incoming user. --> section enables configuration of what to do if/when an unhandled error 开发者_开发百科occurs during the execution of a request. Specifically, it enables developers to configure html error pages to be displayed in place of a error stack trace.

    <customErrors mode="RemoteOnly" defaultRedirect="GenericErrorPage.htm">
        <error statusCode="403" redirect="NoAccess.htm" />
        <error statusCode="404" redirect="FileNotFound.htm" />
    </customErrors>
    -->

You need to check your reference to System.dll. On my machine (and most I would guess) it's at C:\Windows\Microsoft.NET\Framework\v2.0.50727\System.dll.