Error Description:

Msg 17545, Level 16, State 1:
Server 'SYB_ASE', Procedure 'sp_dropuser', Line 267:
You cannot drop user because user 'testuser' owns objects in database.

Resolution:

Step1: First find out uid of user

1> select uid from sysusers where suid = suser_id('testuser')
2> go
uid=220

Step2: Updating Sysobjects

update sysobjects set uid=1 where uid=220

Step3: Drop User

1> sp_dropuser testuser
2> go
User has been dropped from current database.
(return status = 0)
1> exit