iCal keeps quitting...what to do??

I had my iCal synced with Google Calendar, which worked for a while but often resulted in me getting numerous reminder emails through Mail (which I never use). These would display the reminder msg, without actually sending it through, and clogging up my screen with numerous 'draft' reminders, which I would have to delete individually, taking up a lot of time!! So I tried to solve the problem by deleting the mailbox on Mail which would filter Google Calendar. Now iCal and Google Calendar wont sync, and iCal itself keeps quitting every 2 mins, and continually asks me to verify my user details. I can't figure this one out! please help!

OS version?