Yes I have seen these articles and my configuration follows Microsofts guidelines. I do at the moment have netbios ports open but I don't know if that is necessary. However to make my problem clear, my firewall is not blocking anything and doesn't appear to be the problem.The vast majority of the times, everything works fine but in sporadic instances the DS stops reponding to the clients and so the client needs to start the conversation over. As far as I can see this is always after the RPC directs the clients to use the appropriate port for the DS.
List Charter and FAQ at: http://www.sunbelt-software.com/exchange_list_charter.htm
