Client route to Exchange Server wrong

If anyone can help with this I would be greatful. The company that I work for has 8 remote sites and a 4.0 bdc at each site. The PDC is at the HQ building, there are also some W2K member servers at HQ mixed in. Once in a while, in a remote site, a user will not be able to get into the Exchange 5.5 Server at HQ. They are able to ping other servers (locally and at HQ) but not the Exchange Server. The routing table has the wrong info in it for the client computer. Once you delete the route, it works fine again. Is there a way to stop the routing table from getting incorrect routes?