Have BES Admin send you a service book and see if that will help with your calendar synchronization issue. If that doesn’t work… try these steps:
1. Launch BlackBerry Desktop Manager without connecting the BlackBerry handheld.
Select Intellisync within BlackBerry Desktop Manager and make sure that under Auto start... that Synchronize PIM is not checked.
2. Connect BlackBerry to computer
3. Select Backup and Restore within BlackBerry Desktop Manager
4. Backup your BlackBerry
5. Select Intellisync within BlackBerry Desktop Manager.
6. Select the Configure PIM button
7. If you're on wireless sync for the calender, change your sync to local (i.e. MS Outlook)
8. Select Backup/Restore within BlackBerry Desktop Manager
9. Select the Advance button
10. Delete your calendar data from the right hand side which is the local data by clicking on the Calendar entry on the right and then pressing the Clear button
11. Select Intellisync within BlackBerry Desktop Manager
12. Select the Configure PIM button
13. Change your local sync back to BlackBerry wireless sync
It will take a few minutes by the Calendar will re-synchronize wirelessly.
14. If the above fails, you can try to Reactivate by using Enterprise Activation
Hope this help if you haven't tried it yet,