“There was an error saving iCal data” error message

After updating to Lion, I occassionally get this error message when creating or editing events in iCal:

"There was an error saving iCal data. iCal encountered a critical error while saving to the database, and recent changes may be lost. More information may be available in the console."

When I get this error, I am unable to change or delete the glitchy event. Other events are able to be changed or deleted normally. If I quit and relaunch iCal, then I am able to change the events, but this sounds like a very Windows-like solution to a problem.

Not sure if it matters, but I sync my iCal with an iPad 2. Any ideas about what this error is all about?