In a SQL Server 2005 database, I was having a hard time deleting a user I had created.
I kept getting this error:
The database principal owns a database role and cannot be dropped. Msg 15421.
MSDN and Google were not helpful on this error. Ater lots of search attempts I kept coming up empty:

I spent some time looking through various dialogs in SQL Server Management Studio. I was unable to find the problem - probably because I am not as familiar with the UI as I was with Enterprise Manager.