Weird RegAsm Error

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I have an exe which requires a dll to run. When registering the dll, i getthis error:

RegAsm error: Could not load type 'System.Runtime.CompilerServices.RuntimeCompatibilityAttribute' from assembly 'mscorlb, Version=2.0.3600.0, Culture = neutral, PublicKeyToken = b77a5c561934e089'.

Although I get this error, the dll is still registered, and the program DOES work.

Any ideas on how to remove this error?