Annual recurring events like birthdays are duplicated when sync

Suddenly all one-day, annual and other recurring events like birthdays were duplicated in my Outlook 2011 after a sync.

I spend hours cleaning the calendar and when I sync again... after a couple of syncs again they are duplicated!!!

I also try rebuilding the identity and... the same problem...

Besides, iTunes syncing is way too slow and is taking a long time to sync calendar and contact... maybe there is a corrupt file somewhere...

any thoughts????

Question about Outlook Express