Oracle AQ fail to dequeue

Hi,

I have set up aq to send message between two database.
I have used the AQ's message propagation feature. However, the message has successfully arrived at destination database's queue, but the dequeue process does not work.

Meaning the registered stored procedure, which is registered using DBMS_AQ.register procedure, is not called when the message is arrived at destination database.

Any guideline to debug and what is the possible cause to this problem?

Many many thanks!