Drop User With Msg 15138?

Hi: I try to drop a user with following error
drop user TestUser
Msg 15138, Level 16, State 1, Line 1
The database principal owns a schema in the database, and cannot be dropped.

Then I tried:
select * from information_schema.schemata
where schema_owner = 'TestUser'
CATALOG_NAME SCHEMA_NAME SCHEMA_OWNER
---------------- ------------- ------------
DB_Installation db_datareader TestUser
(1 row(s) affected)

Drop schema TestUser
Msg 15151, Level 16, State 1, Line 1
Cannot drop the schema 'TestUser', because it does not exist or you do not have permission.

any idea?
thanks
-D