Iphone syc with computer fails

Help! I'm running Snow Leopard on Imac with Itunes 10.7 I'm using a 3G Iphone. It quit syncing after a sync with my office computer using MiniMac with same system software. I tried deleting device backup and it then allowed a sync but failed to sync calendars. I've also had recurring problem of the sync adding scores of notes to contacts where I had notes and duplicating calendar events in the past. Anyone have an answer??