We have Exchange 2003 and recently we started to get a lot of complains of people Iphones/Ipads to sync their Calendars.
Emails sync normally but Calendars do not.
Our workaround is move all the meeting requests and appointments from the main "Calendar" to another calendar called "Backup Calendar".
Finally we moved everything back to the main "Calendar" in block of 100 meetings. If we move the whole thing just once, the device does not sync. If we move in parts, it works.
We suspect after our customers upgrade their Apple SO to 5.11, this problem started.
On our front-end, we are getting the following Critical error in the Application Event Viewer>>
Event Id: 3005
Description: Unexpected Exchange mailbox Server error: Server: [backEnd server] User: [email@example.com]
HTTP status code: .
Verify that the Exchange mailbox Server is working correctly.
For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp