We’ve been researching calendar issues with Outlook and iPhones, including duplicate appointments, missing appointments, changes in Outlook not showing up on IOS devices, etc. Microsoft and Apple do not have fixes for the problems. They do have recommendations. I’ve copied below some suggestions from Microsoft, University of Iowa, and University of Virginia, who were having similar issues.

If you've noticed missing calendar appointments (e.g., lost meetings, delegate issues), or meeting updates from someone other than the original organizer, you're not alone. These issues have been reported in organizations with Microsoft Exchange, Outlook (2003, 2007, 2010 or 2013), Apple iPhones/iPads/iPods, Active Sync devices, Apple Macs running Entourage or Outlook 2011, and RIM Blackberries.

Exchange itself is usually not the root of the problem, the mail clients (ActiveSync, iOS devices, Blackberries, iCal) and their connectivity protocol tend to be the culprits. Another cause of the issue is sync timing. For instance, if someone accepts a meeting at 9am on an iPhone and a delegate declines it at 9:10am on a PC, but the iPhone is out of signal range and doesn't sync the meeting until say 9:30am., what happens to the meeting?

There is no simple solution, but the following tips may lessen the frequency of calendaring issues:

Run the same version of Outlook on all of your computers, at work and at home. Mailbox owners and any delegates should be using the same version of Outlook with the latest service pack and updates on all computers that are used for calendaring. If you are in a mixed environment of Windows, Mac or mobile devices, each platform should use the same version and each device should have the latest service pack and updates.

Only one person should process meeting requests. Other people, computers or devices that recieve the meeting request should ignore them, i.e. leave them be, do not delete them do not process them.

Have no more than two delegates.

Manage your calendar exclusively from Outlook or OWA. Don't accept, decline, modify or invite others to appointments from your mobile device. You can, however, create new appointments on your mobile device, (e.g., add one while checking out at a doctor's office).

To change an entire series of meetings, cancel the original meeting and create a new one. To change one instance, cancel just that meeting and create a new one to replace it. Always put an end date on a recurring meeting.

A "corrupt" meeting will remain that way until you delete it. If it is a recurring appointment, delete all occurences and reschedule it.
When scheduling a recurring meeting, Microsoft recommends setting the end date no more than 6 months. If you need to schedule a meeting for a longer period, start a new recurring meeting.

Do not drag and drop meetings to change the time or day. Open the meeting, make the desired changes and save it.

Make sure your mobile device has the latest OS/iOS version. Often new devices do not, so be sure to check for updates. Be sure to sync, or back up your device before updating the OS. If you’re not sure how to do this, contact the Helpdesk. We will have a Technician check to ensure your Outlook and mobile devices are all running the latest version.

Make sure the Calendar on your IOS device is showing only the Outlook calendar. Duplicates can show up if more than on e calendar is displayed. Click “Calendars” at the bottom of the Calendar app to see which calendars are being displayed. Only your primary calendar under “All Exchange Calendars” should be checked.

Computing Services is planning to upgrade Exchange to version 2013 in the next few months. This may help to alleviate some of the issues as well.

Contact the Helpdesk if you have any further questions or to report calendar issues.