I know this thread is over a year old, but if you google "blackberry not synching with Outlook calendar" you might end up here. From my experience, this is the result of at least one but up to all of the following being true:
1) cdo.dll is not registered. This page from BB tells you which version of cdo.dll matches which version of mapi32 matches which version of Exchange. Very handy: BlackBerry Search Results
2) CDO.dll is registered in the wrong folder. DO NOT COPY AND REGISTER IT IN SYSTEM32 FOLDER. Register it (regsvr32 cdo.dll) in the Bin folder under the Exchange folder. To check where it is registered, ref the following article: BlackBerry Search Results
If it is registered in the incorrect location, re-register and restart the Dispatcher service.
3) Here was my problem: Service account has incorrect rights in Exchange. Our service account was a member of the domain admins group. You may think that will ensure the account has adequate permissions in Exchange, but you'd be wrong. In Exchange 2003, domain admins are by default denied the right to Send As and Receive As, a right which the blackberry service account MUST have. You'll either need to remove the blackberry service account from domain admins, or adjust the exchange permissions accordingly. If you need additional info on doing that, let me know.
Hope this helps.