iphone 5 - only one way synchronization with iCal

Hello community,

Since I have my new iPhone 5 the calendar synchronization is not working properly anymore which means only one way from iCal to iPhone but not the other direction. I could not found a solution in the diverse support communities so maybe you have an idea what the error might be?

I am synchronizing locally via iTunes from a Mac Book Pro and I am not using iCloud.

It would be great if you could help.

Greetings from Zurich,

Heike Anna