I'm assuming BIS....
I'm also just guessing at possibilities:
Do another hard rest. Be sure you remove the battery with the power on. And this time wait two or three minutes. Then test.
If that did do it, try deleting the CICAL service books, then do a hard reset, and then re-send service books. (See How do I resend my service books? - BlackBerryFAQ
). This is just a SWAG, given that deleting the calendars and recreating them may eleminate some glitch. You won't lose any data, but still do a backup first, just to be safe.
If that didn't do it, try deteting the calendar data bases using Desktop Manager, then test before you restore your calendar data from backup. Again, just a SWAG.
If you still have trouble, maybe you need to re-install the OS. But see what others say before you go that far. Posted via BlackBerryForums.com Mobile