Will you please try to identify schemas owned by that user using:
SELECT s.name SchemaName, d.name SchemaOwnerName FROM sys.schemas s INNER JOIN sys.database_principals d ON s.principal_id= d.principal_id
And transfering the respective ownerships to some schema owner (e.g. if kaluk is schema owner of db_datawriter)
ALTER AUTHORIZATION ON SCHEMA::[db_datawriter] TO [db_datawriter]
then try dropping user