HELP!!!! Bouncing Desktop Icon

Hello,

The calendar icon on my imac bounces every time I try to add an event to the calendar. This calendar is synced with our google calendar. I get the following message; The URL https://calendar.google.com/calendar/dav/orthoadvantage@ameritech.net/user///calendar.google.com/calendar/dav/orthoadvantage@ameritech.net/user/ encountered HTTP error 404. Make sure the URL is correct. And then sometimes a box that give an option to revert to server or retry or ignor. I have heard that there should not be a forward slash after "user" in the error messages, but I can't find anywhere to access that in order to change it. I would appreciate ANY HELP.