Registered subscriber not getting messages from queue

We have a process using Oracle AQ on Oracle 11.2. It was working just fine, buy yesterday, messages in the queue stopped getting dispatched to the subscriber. Here is the setup we have to create the queue and register the handler:

<span class="pln" style="background: none transparent scroll repeat 0% 0%; color: #000000; font-size: 14px;">DBMS_AQADM</span><span class="pun" style="background: none transparent scroll repeat 0% 0%; color: #000000; font-size: 14px;">.</span><span class="pln" style="background: none transparent scroll repeat 0% 0%; color: #000000; font-size: 14px;">CREATE_QUEUE_TABLE </span><span class="pun" style="background: none transparent scroll repeat 0% 0%; color: #000000; font-size: 14px;">(</span><span class="pln" style="background: none transparent scroll repeat 0% 0%; color: #000000; font-size: 14px;"><br/>  queue_table  </span><span class="pun" style="background: none transparent scroll repeat 0% 0%; color: #000000; font-size: 14px;">=></span><span class="pln" style="background: none transparent scroll repeat 0% 0%; color: #000000; font-size: 14px;"> </span><span class="str" style="background: none transparent scroll repeat 0% 0%; color: #800000; font-size: