The Upgrade Advisor detected user-defined functions that are owned by the undocumented user system_function_schema. In SQL ...

The Upgrade Advisor detected user-defined functions that are owned by the undocumented user system_function_schema. In SQL Server 2000, you can create a user-defined system function by specifying this user; however, in SQL Server 2005 and later, this action is not permitted. The system_function_schema user name does not exist, and the user ID that is associated with this name (UID = 4) is reserved for the sys schema and is restricted to internal use only.