SQL Server: An error occurred while generating an asymmetric key

CREATE ASYMMETRIC KEY asymmetrickey 
FROM EXECUTABLE FILE = 'c:\windows\microsoft.net\framework\v2.0.50727\system.windows.forms.dll'

      

        
        
        
      

    

Why can't I use the above to generate an asymmetric key from the frame libraries (to be installed on SQL server as references for CLR functions). This gives an error:

"An error occurred while generating an asymmetric key."

Without an asymmetric key, the database must be configured to add the assembly in SQL Server (2005). I understand that framework libraries are not meant to be used with SQL Server, but I am wondering why this is not working.