Problem: Have multiple users that share an Exchange 2010 calendar. After we switched out their iPhone’s and added the shared calendar, it did not show up in the calendar view and wasn’t able to select it when choosing which calendars to view. Tried restarting the iPhone, resetting the account and tried the Outlook app without any luck.
Solution: Turns out that you have a limit of 10 devices that can sync with the account so I had to go into OWA and remove old devices. You can also remove devices in Exchange Management Console using the “Manage mobile phone..” option.