you must stop and drop all the queues in a queue tables before the queue table can be dropped. You must do this explicitly unless the force option is used in which case this done automatically.
Syntax:
DBMS_AQADM.DROP_QUEUE_TABLE (
queue_table IN VARCHAR2,
force IN BOOLEAN default FALSE,
auto_commit IN BOOLEAN default TRUE);
The operation will not succeed if there are any queues in the table.This is the default.
Make the force as TRUE: All queues in the table are stopped and dropped automatically.
From the PL/SQL :
EXECUTE dbms_aqadm.drop_queue_table (
queue_table => 'aq.Objmsgs_qtab',
force => TRUE);