Why did I get an ORA-08103: object no longer exists error message?

It just so happens that I was waiting for an Oracle Alert to come out, but the request had errored and I was presented with "ORA-08103: object no longer exists" which did not make a whole lot of sense.  I started thinking back to what could have caused this, and I realized that this Alert was looking to query from objects in our BPEL environment but at the time it was supposed to query from the AQ (Advanced Queue) we bounced the BPEL consumer.  This does not seem correct as BPEL is supposed to be a passthrough, and the AQ should be on another non-BPEL system, so I do not understand why the Alert needed the BPEL consumer to be up for it to be able to query the non-BPEL AQ.  Another mystery!