Users with iOS devices (i.e. iPads & iPhones) are unable to Accept/Decline Calendar Invitations directly through their iOS devices.
When they receive the Invitation, and open the ICS file through the Mail app, the "Maybe", "Decline", and "Accept" Buttons are missing from the bottom of the screen.
When they then open their Calendar app, they can see an Invitation waiting in the corner of their screen - and when they click on the icon, they can see the Invitation.
However, the Invitation is missing the sender information (just displays "From: somebody"). When the user attempts to use the "Maybe", "Decline", "Accept" buttons which appear directly underneath the invitation details, nothing happens - the Invitation does not process and it remains marked tentative in the user's calendar.
Notes:
- I've tried running the command "Set-CalendarProcessing -Identity [username] -AutomateProcessing autoupdate" through PowerShell on one of the affect users - this had no affect and the issue still remains.
- This only appears to affect Office 365 mailboxes. When I tried to reproduce this issue with a separate iOS device (iPhone 4S - iOS 6.0.1) on a separate Exchange 2007 server, I was able to correctly Accept/Decline the invitation on the iOS device.