ORA-16621: database name for ADD DATABASE must be unique
Cause : An attempt was made to add a database to the broker configuration that already includes a database with the specified name. The database names must be unique.
Action - How to fix it : DBA Scripts :: www.high-oracle.com/scripts
Verify that you have specified a unique name for the new database you wish to add. This can be done by checking that there is no database with the same name. Also note that the database name must match the DB_UNIQUE_NAME initialization parameter of the database.
Well, the reason for above error is that i have taken the above script from a 11g database and running it on 10g database. 11g has bring some changes in password management. Below code is executed on 11g and user created successfully, which is expected result.