Still a problem; still no solution?
Same thing happening to me... and it breaks MobileMe sync. I'm told by Apple Support that my iCal file is too large to sync, so I should delete older events via the auto-delete settings in Preferences.
I'd be willing to that, but iCal doesn't delete the old events.
I've tried the tip of searching for, as an example, the letter "a", then deleting 1 or more of the events in search results. iCal locks up for a very long time, seems to have deleted them, but, when I restart iCal, they are still there. I've tried with one event, a few, and a few dozen at once.
I just don't know what to do. The MobileMe sync feature, remains useless to me since late February. The only solutions I see proposed, here or elsewhere, have failed.