This problem occurs when the client computer that is running Windows XP releases the remote COM+ object. Approximately 20 seconds to 30 seconds after the client computer releases the remote COM+ object, the RPC ports that were used by DCOM on the server are closed. If the network is disconnected immediately after the client computer releases the remote COM+ object, the RPC ports that were used by DCOM on the server remain open for several hours. This can lead to port exhaustion. Future requests from the client computer to the remote COM+ object fail.
This is corrected with a hotfix from microsoft...see below and let me know if this works.
http://support.microsoft.com/default.aspx/kb/935677
BrianM - MCSE,MCSA,MCTS,A+,NET+,SEC+
Toronto, On.