Wirelessly posted (Mozilla/5.0 (iPod; U; CPU iPhone OS 2_1_1 like Mac OS X; en-us) AppleWebKit/525.18.1 (KHTML, like Gecko) Version/3.1.1 Mobile/5F138 Safari/525.20)
When it happened to me I merely cancelled the sync and then reconnected, havent had the problem since. Perhaps try a restore or disable syncing calendars, sync, then enable it again.