You may receive this error when syncing with Google since December of 2009. This error occurs when Google's servers respond with a "Server Error" message. In the past we have seen this error occur for a few days after we release an upgrade but in more recent times this error has been more common.
After talking with Google engineers regarding their server error we have found that the primary cause of this error are Google Calendar accounts that contain a subscription to "Remember the Milk". These calendar subscriptions will cause Google's calendar API servers to fail more often than not. To fix this error you must completely remove the subscription from your account. It is not good enough to disable or ignore the calendar. We have had some reports of people having to unsubscribe multiple times for the change to "stick".
Google is aware of the bug causing this problem to occur and has a fix in the works. However we do not have any dates available to us from them as to when this fix will be put into production on their servers.