This link may be able to help explain the problem. Error message received when integrating a Microsoft Outlook Web Access 2003 or 2007 account
I'm having the same problem, and the above link seems to match most closely with my situation. I too do not have control of the exchange server environment, so have my hands are tied.
An alternative to consider is setting up an Outlook 'mail redirect' rule and tweaking it to your liking. This is what I'm currently doing to get my mail onto my BBerry. It takes some time to get set up just the way you want it, and doesn't provide the full feature set of a BES, but works okay for mail. You may also consider using a Google Calendar and Google's free Google Sync program to sync your BBerry Calendar OTA, but I digress.
Best of luck, and maybe RIM will resolve this issue soon for the rest of us as well.