Sudden problem syncing calendar

[iwolgca]

Hi everyone, I'm new here and hope someone can help me out. I have an iPhone 3Gs and sync my calendar and notes with my Mac OS 10.5.8 iCal and Mail. Somehow, my iPhone lost all the events on my calendar. They are still in iCal but will not transfer to my mobile. How can I restore that part of my synchronization? I was unable to sync my Notes at the same time. This has not happened before but occurred just prior to updating the iPHone OS 4.0.

Thanks