Is this issue only with VPN connections? Is the Outlook session successful when attached locally to the network? If managing your servers remotely, do any of the non Exchange servers have Outlook installed. It is fairly simple to give an administrator account access to your mailbox, and then test with the previously mentioned Outlook installation.
As for your VPN connected computer.....
Try starting Outlook in "Safe Mode" to isolate whether an add in is interfering. You do this by holding down the Ctrl key while Outlook starts up. You will be prompted for stating Outlook in safe mode.
You can also try creating another Outlook profile and seeing if the new profile has better success retrieving your mail. A failure in creating a new profile over the VPN connection could indicate some interference from the VPN client.
The fact that you can see your mail in OWA indicates that the Exchange mail store is reasonably intact. Please try the other suggestions above before probing the mail store for corruption. I once had a voicemail server that was not syncing with Exchange correctly for one user. I had to use ESESUTIL and ISINTEG to straighten out the problem for one corrupted mailbox. I have posted some links regarding these utilities here:
https://www-secure.symantec.com/connect/forums/besr-85-how-do-i-restore-exchange-2003-information-store
You only want use these utilities as a last resort on a production server because you do have to dismount the mail stores in order to use them.
