iTunes won't see and sync my calendars

Hi all,

I have the following problem: iTunes doesn't recognize my calendars and therefore doesn't sync them. The calendar dialog in iTunes looks like this:

And my calendars look like that:

All attemps to fix that have failed so far. I have exported, deleted and re-imported calendars, deleted Library/Calendars as well as Library/Application Support/SyncServices - without any change.

I'm close to desperation, in particular since I'm right before a business travel and I will need my calendars on the iPhone.

My system data:

MacBook Pro Retina with MacOS X 10.8.5
iTunes 11.1.2

iPhone 5 running iOS 7.0.3.

Any idea how to get this to work again is greatly appreciated!

Thanks in advance + best wishes,

Thomas.