ORA-24177
Another purge_queue_table session (sid string, serial# string) is already active on the same queue table
Cause
An attempt was made to run DBMS_AQADM.PURGE_QUEUE_TABLE in parallel when one purge_queue_table session is already active on the same queue table.
Action
Only one purge_queue_table session can be active at a time on a queue table. Wait for the active session to finish before spawning another purge_queue_table session.