Problem
Recently I had an issue while dropping an orphaned user for an obsolete login. I was unable to drop the user and it failed with the below error messages.

Msg 15421, Level 16, State 1, Line 1
The database principal owns a database role and cannot be dropped.
Msg 15138, Level 16, State 1, Line 1
The database principal owns a schema in the database, and cannot be dropped.</code

Solution
http://www.mssqltips.com/sqlservertip/2620/steps-to-drop-an-orphan-sql-server-user-when-it-owns-a-schema-or-role/