ical The Server is Busy or Unavailable?

How do I resolve the following problem with ical:

The Server is Busy or Unavailable.

The server is currently unable to handle the connection due to a temporary overloading or maintenance of the server. If this continues you should contact the server administrator.

You may try to connect to the server again or take the account offline.

This has been going on for a while and cannot find a way to stop.

Any help would be appreaciated.

Dennis