After installing some application that needs the .Net Framework 1.1 (I had 2.0 already installed) my SQL Server Management Studio (2005) begins to complain about not finding mscorlib.tbl the message was:
The file C:\Windows\Microsoft.NET\Framework\[version_number]\mscorlib.tlb could not be loaded.
It seems that an environment variable was deleted or lost.
To correct that there is a workaround from Microsoft (KB918685), but I think it’s better to add the removed variable.
Right clicking my computer, properties, advanced, environment variables and then (for 2005) add the variable with name and value:
Check with your terminal (console/command prompt)