Q: Error with Calendar

Can anyone help with the following error that shows when calendar opens:

"The server responded with an error.

The URL https://p02-caldav.icloud.com/1384090887/principal/ encountered HTTP error 404. Make sure the URL is correct."

I cannot find any solution to this anywhere and have no idea how to check the URL or change it if it wrong nor what the correct one is !

Any help appreciated