Hi Becki,

iCal calendars don't talk to Totara. You need to teach your users to log into Totara and cancel their seminar signups that way. The event will still be in their calendar, with status "not attending" (or similar) but they're still booked to attend that session. When they cancel in Totara, they'll get another notification with ical which will remove the calendar entry.

regards,

George.