iCal locked up w/ 'The server responded with an error.'

I created a new reminder which I believe was too long so it didn’t process but instead 'The server responded with an error,’ appears in a separate window imposed on the calendar and containing the entire long reminder but freezing the iCal program so I cannot go to preferences and change anything. I have to force quit iCal and try & try again, but each time within seconds the message reappears and all is frozen. HELP PLEASE.