In order to open someone else's calendar when you don't have full permissions to their hierarchy, you have to use certain tricks to locate the calendar. One of these tricks is that Outlook will record the location (entry ID) of the calendar in a special property located on the Inbox folder. Delegates trying to open this user's calendar will look for this entry ID, then try to open it. If the entry ID happens to be incorrect, then we can't find the folder.
I bet you see a similar failure if you try to use Outlook to open this particular user's calendar folder.
Most likely, if this user runs Outlook with the /resetfolders or /resetfoldernames switch, Outlook will rewrite the Calendar pointer and you should be able to then open it.
I bet you see a similar failure if you try to use Outlook to open this particular user's calendar folder.
Most likely, if this user runs Outlook with the /resetfolders or /resetfoldernames switch, Outlook will rewrite the Calendar pointer and you should be able to then open it.