I've found that if the JBoss server is busy such that an a4j:poll is waiting for response, if the user clicks away to another page he gets an error code 599 (in A4J.AJAX.onError) and a4j:poll then stops working for all pages in that browser. The user can go to pages that have a4j:poll but the poll never runs on any of them from that point. The onlly solution appears to be to shutdown the browser and restart it. I'm using Richfaces 3.3.3.Final and FF 3.6.13 (JBoss 6.0.0_Final AS).
Is there a work around? Is there a way to restart polling?