turns out the trailing slash is important. (the original issue that led me here was that my akonadi (kde/kdepim 4) resource was complaining about something or other; but seems that complaint isn't preventing it from reading the calendar via caldav)
I've run into the same problem. We've got a company exchange server, and caldav seems to have stopped working. When I go to e.g. http://localhost:1080/users/myuser@mycompany.com/calendar it comes back with: calendar not found in /users/myuser@mycompany.com.