iCal no longer syncing with iPhone

My iCal has suddenly stopped syncing with my iPhone and I have tried everything to get it to work again, with no luck. I do not use iCloud and sync through iTunes.

The operating system on my computer is Mountain Lion, my iPhone is a 4S with iSO 5.1.1 and I am using iTunes 11.0.1.

Does anyone know what could be causing my syncing to suddenly stop? Everything else on my computer is syncing with my iPhone.