We are not able browse internal websites from our Blackberry devices

We have just migrated to a new BES server (WinServer 2008, Exchange 2003, BES 5.0.3). Our problem is that we are unable to browse internal websites from our bb devices. We are always routed to external sites. Only MDS Browser is enabled! There have been a few occasions during our testing (alone and with BES Tech Support) where the browser did go to the internal sites but on the next attempt it would take us to an external site with the same URL (this external site does not belong to our company!). Has anyone had experience with this issue. I have already tried changing the configuration under proxy mappings (added our internal URL, tried providing our proxyserver:8080, and also tried using a direct connection. Catch all has been used and is still in the list but nothing seems to work. Logs have been forwarded to BES Tech Support but they also have no idea what the problem could be. If anyone has any advice on this issue or even thinks you may know the cause, please respond. Thank you.

Use your blackberry When You Travel Unlock it now
Use Your Blackberry on Any Network