This morning we fixed a problem that has been preventing some users from syncing very large calendars (with thousands of events) from iCal to Google Calendar. Calendars too large to sync in a single operation will now be spread across multiple sync cycles. No download is required to take advantage of the fix.
Please note that Google has been experiencing sporadic problems today affecting not only Calendar but also other applications including Blogger and Google Apps Partner Pages. If you see any Spanning Sync error messages, please wait a few minutes and try again. If the problem persists, please contact email@example.com.