If you encounter following error message



in Sql Server Management Studio, you should check two things:

The problem might arrise if you restore a database on your Sql Server and the Database Compatibility Level is not set to 90. Try to switch the level via Database Properties. This can also be done with T-SQL like this:

EXEC sp_dbcmptlevel ’databasename’, 90

If the problem persists you should do a

ALTER AUTHORIZATION ON DATABASE::databasename TO [domain\user]

because in Sql Server Management Studio (without SP1) you cannot set the database owner to the correct login via Database Properties - or better said the Management Studio actually displays either the correct User - yet it recognises it as invalid or it displays the original User and cannot map it to the current server because it doesn’t find a corresponding SSID.