Mscorlib.dll is in GAC now in .Net framework 2.0, contrast to v1.0/v1.1, where mscorlib is in framework's directory.
If you rely on mscorlib.dll's path to get framework's directory, you have to change your code to use System.Runtime.IneropServices.RuntimeEnvironment.GetRuntimeDirectory, which also exists in v1.1.
C:\>gacutil -l mscorlib
Microsoft (R) .NET Global Assembly Cache Utility. Version 2.0.40607.16
Copyright (C) Microsoft Corporation. All rights reserved.
The Global Assembly Cache contains the following assemblies:
mscorlib, Version=2.0.3600.0, Culture=neutral, PublicKeyToken=b77a5c561934e089, ProcessorArchitecture=x86
Number of items = 1