Calendar will no longer sync with iPhone

My calendar would sync with no problems and now it won't update the information on my iphone so I am stuck with the old information and having to manually update the calendar.

Please help.

Using version 6.0 of calendar

Using version 10.7 of iTunes

Using 6.0.1 on iPhone

Using OS X 10.8.2

Everything says it's up to date. When I attempt to sync, nothing changes on the calendar.

Thank you,

Amy