can't sync Calendar events from Mac to iPhone Mac running OS X 10.8.1, and iPhone 4 running 5.1.1. Since upgrading to OS X 10.8.1 from 10.7.4, I can't sync Calendar events from the Mac to the iPhone. The opposite direction works just fine. I am using iTunes for the sync via USB, all calendars are checked in iTunes to be synced.

Any idea what may be going wrong?
Ok, after looking at some error entries in system.log I found a link to this Apple KB article: Mac OS X: Resetting the SyncServices folder, which solved my problem. It is important not only to reset the sync services, but also to enable them after that as shown at the end of the KB article.