Calendar server error: "The server responded with an error. There is insufficient storage space for “New Event” in “xxxx iCal” in account “MobileMe”"

When I opened my iCal app on my iMac it has the triangle with an exclamation point next to the MobileMe account. Clicking on the icon produces the following: "The server responded with an error. There is insufficient storage space for “New Event” in “xxxx iCal” in account “MobileMe”"

How do I fix this? When I press "revert to server" the error goes away and reappears 5 seconds later.

This is across all of my macs and is a huge issue. Help!