I have an Exchange account that is set to Email, Contacts and Calendars, but for some reason it won't work correctly after upgrading my iPhone 4 to IOS6.
I've deleted the account and added it again, just to make sure I start from nothing. After adding the account the calendar events won't show up. If I reboot the phone, they show up, but after maybe 15 minutes (Which is what I set the update interval to. I've also tried using push), the calender has been unchecked. If I check it again, the events won't reappear, and after some time (maybe 15 minutes, haven't timed it) the calendar is unchecked again.