QUICK WORKAROUND, EITHER CREATE AN OUTLOOK PROFILE FOR THE MAILBOX IN QUESTION AND SET THE PERMISSIONS ON THE CALENDAR THERE. THE OTHER METHOD IS LOG INTO THE MAILBOX VIA OWA AND SHARE THE CALENDAR THERE. I GUESS THIS IS A BUG OR GLITCH SIMPLY BECAUSE I DID NOT FIND A SOLUTION ON THE WEB. SORRY IF I ANNOYED ANYONE WITH THE DETAILS BELOW. MY CUSTOMER HAD DONE EVERYTHING CORRECTLY AS FAR AS HAVING FULL CONTROL, TOP DOWN PERSMISSIONS, ETC..
I ran into this problem yesterday. I could not find any solution on the web, which was surprising. I saw many complaints, but no solution that worked. In my customers situation they were adding additional mailboxes to their Exchange 2010 profiles and using Outlook 2007. They simply wanted to share only the Calendar of a mailbox named BIDS. You could go and set all the various permissions for the various users. Permissions looked fine, but when you clicked okay "an error occurred when setting schedule permissions" would appear. On the users computers/profiles that had the additional mailbox added, they would get a free/busy error and could not use the calendar. I checked the stuff about delegates and it did not pertain. I noticed this problem did not occur when sharing the primary mailbox calendar in the Outlook profile. So, I simply added another profile for the BIDS mailbox, checked the permissions on the Calendar, they looked the same, just fine. Clicked OK, no error then it all worked fine for all the users that had been given permission. They had several mailbox calendars they need to function in the same manner, and all had this problem. I am lazy, so I decided to log into OWA and set the permissions there, rather than creating more profiles. However, in OWA there is an option when you right click on the calendar, to "change sharing permissions". You can only see who has been given permission and delete members, but not add. Quite annoying, so I clicked "share this calendar" and you can add additional members, and the exisitng members/permissions stay in place.
Edited by colmanryan, 08 June 2010 - 11:11 PM.