Description of the problem: When you tried to drop a user, you got this message:

Error: 15138 The database principal owns a schema in the database, and cannot be dropped.

Cause: That means, you are trying to drop a user owning a schema. In order to drop the user, you have to find the schema that’s assigned and then transfer the ownership to another user/role or to drop it.

Resolution: You can fix the issue following two ways.


By script: You can find out which schema is owned by this user with the query below:

SELECT name FROM  sys.schemas WHERE principal_id = USER_ID('myUser')

Then, use the names found from the above query below in place of the SchemaName below. And drop your user.
   
ALTER AUTHORIZATION ON SCHEMA::SchemaName TO dbo
GO
DROP USER myUser

By Management Studio:

- Object Explorer >> Expand the [databasename] >> Security.
- Click on Schemas.
- In summary window, determine which Schema(s) are owned by the user and either change the owner or remove the Scheme(s).
- If they are system schema(s), I suggest to change them to ‘dbo’.
- Drop your user.

More detail about schemas into the BOL:
http://msdn2.microsoft.com/en-us/library/ms190387.aspx

Michel Degremont | Premier Field Engineer - SQL Server Core Engineer |