Whilst removing orphaned user accounts, I came across this error …
Msg 15138, Level 16, State 1, Line 1
The database principal owns a schema in the database, and cannot be dropped.
Looking at the properties of the user within the database I noticed that they owned the db_datawriter schema. Within the properties of that schema I was able to type db_datawriter as the new owner. After which I was able to remove the user from the database.
Here is a scripted way to do this …
https://www.mssqltips.com/sqlservertip/3439/script-to-drop-all-orphaned-sql-server-database-users/
Database Consultant 