After upgrading SQL Server, you will also need to update (using Alter Assembly) any .NET Framework assemblies which are not ...

After upgrading SQL Server, you will also need to update (using Alter Assembly) any .NET Framework assemblies which are not on the approved list but have been cataloged in the database. .NET Framework assemblies in the GAC must match the assemblies in the database.  When .NET is upgraded, the version of assemblies in the database must match the version of .NET SQL Server is using.  This is not done automatically since persistent data may be relying upon those assemblies.  This is only an issue for those assemblies not approved for use in SAFE assemblies.  Please refer to Microsoft Knowledge Base Article 949080.