ASP.NET pages are damaged after installing WindowsXP SP 1

Hi !
I have gotten a problem after installing WindowsXP SP1. It is that all of my ASP projects can't execute. It occurs error as following:Server Error in '/Test' Application.
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Compilation Error
Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately.

Compiler Error Message: CS1595: 'System.Runtime.CompilerServices.CompilerGlobalScopeAttribute' is defined in multiple places; using definition from 'C:\windows\microsoft.net\framework\v1.0.3705\mscorlib.dll'

Source Error:



Line 25:
Line 26:
Line 27: [System.Runtime.CompilerServices.CompilerGlobalScopeAttribute()]
Line 28: public class Global_asax : Test.Global {
Line 29:


Source File: C:\WINDOWS\Microsoft.NET\Framework\v1.0.3705\Temporary ASP.NET Files\test\8f514d8e\f7be96e7\nlabflfc.0.cs Line: 27

Please help me. Thank you very much