Can't sync from iPhone4 up to iMac.

I'm using MS Entourage 2008 (12.2.0). No problem syncing down from iMac to iPhone. It won't sync UP from iPhone to iMac. I enter an event for say August 16 on my iPhone then run sync thru iTunes, the event will NOT sync UP to my iMac. But, if i add and event for the same day on my iMac then run sync it will sync both events both ways for that date. Any assistance would be appreciated. Thanks.