Originally Posted by OnlyGODSanExpert
RSET usually resolves that issue. How bout trying to resolve using desktop software.
1) Delete your desktop sync service book. Then attach the device to desktop software
2) Full back up (just in case)
3) Delete all calendar databases on your phone ( Device-Delete Data- Calendar All)
4) Remove your device from desktop software. And Un-delete your desktop service book.
This should start a slow sync... only bringing over your single calendar entries from Outlook
Worse case scenario if this does not work would be to remove/wipe/ re-active the device.
OR just simply delete all your calender entries from your phone and perform new synchronization with outlook again.