Hello,
After fighting this thing I found a solution for the "Error from server: Error processing calendar data (210)" that's consistent for me:
After creating the group, adding members, and enabling the wiki and web calendar services, save in Workgroup Manager. Then, in Server Admin, restart the iCal Service and
then restart the Web Service.
It appears that the two services don't re-read the group list while they're running. The iCal service won't show a calendar. The web service won't show the group at all. This also goes for making changes to a group, such as enabling the service where it was previously off.
To check to see if there's a cleander (and to learn a whole lot of other stuff) go to the URL you've given in Server Admin, complete with port:
http://servername.com:8008/
or, for SSL:
https://servername.com:8443/ (<- note the "https" not "http")
In /principals/groups/groupshortname/ it should show something like this:
*Calendar homes:*
*-> /calendars/groups/groupshortname*
If it doesn't, then you need to make sure that the service is turned on for the group in Workgroup Manager and then restart the iCal service in Server Admin.
Hope that helps someone,
-Rob