As some of you may remember, about 8 months ago I had a problem syncing with MS Office 2007. Every time I did a sync I lost the calendar pop ups on my BB. Only way to get them back was to do a wipe on the BB and reload all my data. After working with RIM for almost a month we thought it was a problem with a .pst file. Solution - don't sync with Office.
In the last week or so I started using Google Calendars and their OTA sync program only to find that I'm not getting my pop up reminders again. Yesterday I removed all the entries that were entered using the Google sync, removed both Google Sync and their Mobile Update program. After that I did a battery pull and everything came back to normal.