ORA-01422 ORA-06512 executing dbms_aqadm.add_subscriber

I posted this on the PL/SQL community and go a couple of good replies, but it was recommended that I post it to the Database Adminstration community to get a better reply to it.

This code works on one of our other Oracle databases (version 10.2.0.4), but for one of our databases it returns the errors below

DECLARE

  subscriber sys.aq$_agent;

BEGIN

  subscriber := sys.aq$_agent(name => 'SUBNAME',

                              address => NULL,

                              protocol => NULL);

                             

  dbms_aqadm.remove_subscriber(queue_name => 'QNAME',

                            subscriber => subscriber);

dbms_aqadm.add_subscriber(queue_name => 'QTBL_NAME',

                            subscriber => subscriber,delivery_mode => dbms_aqadm.PERSISTENT_OR_BUFFERED);                           

END