Here is a quick fix that I use from time to time when my calendar stops syncing on my BlackBerry Curve 8830 to BES (BlackBerry Enterprise Server).
1.) Go to Options
2.) Advanced Options
3.) Service Book
4.) Desktop [CICAL]; now once you have this highlighted, hit the “BlackBerry Button” 7 (black or white dots) then click Delete, wait about 3 minutes, then, hit the BlackBerry button again, and select undelete. This should force a resync with you calendar service books. At least this way you won’t have to wipe your blackberry!