Unable to accept calendar appointments

Not sure what's going on here, but over the last couple of weeks a few of us (that I know of) are not able to accept calendar appointments from our iOS devices. They are being sent to our work email address (Exchange 2007), and when we open the appt and tap Accept, it just closes the appt - but no acceptance is ever sent to the organizer, and the invitation is not remove from the Inbox. However, we are able to accept the appointments just fine from our Outlook client.

We are using iOS 6.1.2.

Not sure if this is an iOS issue or an Exchange/Active Sync issue. Note that the devices that are having the issue (again, that I know of) are all configured using the MDM BoxTone, not directly to Active Sync.

When I tap Accept from the iOS device, the appt is NOT added to the calendar anywhere - either on the device or in Outlook. I also just did a test of creating an appt from my iPhone and it was never added to the Outlook calendar (it's on the device calendar) and the person I invited did not receive an invitation.

Note that we also have a weird issue that every day (without fail) at 12:15pm the iOS devices suddenly cannot sync email - we get 'Cannot Get Mail - connection to the server failed'. At the same time, my Outlook client loses connection to the Exchange server. This lasts for maybe 5 minutes, then clears up. I have a ticket open with our Exchange support team for this one.

Any ideas?