A calendar is uniquely determined by its group ID and calendar ID. Both IDs are case-sensitive. If you don't know your group ID or calendar ID, they can be derived from the URL for your calendar. For example, if the URL for your calendar is:
http://www.huntcal.com/cgi/calview.cgi/mygroup/mycal
the group iD is mygroup and the calendar iD is mycal.

The group administrator invented the group ID when the group was created.

To avoid the need to return to this page, consider creating a bookmark, or adding the location to your Favorites after you go to the calendar.