Yes, I too am now beset with the same problem:
+The calendar
https://cal.me.com:8443/principals/users/1.1337456841/ could not be accessed. It may be in use by someone else. Try again later.+
I've spent so much money on trying to find a sync system that works - the last was Plaxo, now I'm trying (again) with MobileMe. £59. Another outlay and for what?
+The calendar
https://cal.me.com:8443/principals/users/1.1337456841/ could not be accessed. It may be in use by someone else. Try again later.+
Am I being ripped off here?
I can only conclude that I must Try Again Later but I'm a busy man, I haven't got time to keep trying again later.
Like other people here, I too have made the switch from Windows to Mac and yet my headaches are the same.