I curse MobileMe, but I rely on MobileMe. So do many Mac users, it’s easy to setup and it generally works. However sometimes your info gets mixed up with duplicates or omissions, or a device in your sync setup can get stuck and won’t send or receive new data.
The basic procedure for resetting sync data involves taking the most complete copy of your data and propagating it through all other systems. Pick one system to become your Primary Mac for the steps below.
First, turn off MobileMe sync on all devices before doing anything else. On Macs, go to System Preferences –> MobileMe, click on the Sync tab, and uncheck Synchronize With MobileMe.
On iPhones and iPads, go to Settings –> Mail, Contacts, Calendars –> MobileMe, and switch off the options for Contacts and Calendars. If the data is good then when prompted choose Keep on My iPhone otherwise pick Delete from My iPhone.
Backup your starting data on the primary Mac next – this is an important point I’ve had to relearn multiple times working with clients. Propagating and merging data across multiple devices can have unintended results, particularly if there’s a system in the chain which you aren’t aware of. Your Contacts and Calendar databases are located in your home folder inside the Library folder, as follows:
Contacts Data: Home Folder –> Library –> Application Support –> AddressBook
Calendar Data: Home Folder –> Library –> Calendars
Select each folder and copy using the Finder’s Duplicate option (Command-D). For extra safety, also copy these folders to to another disk or a USB flash drive. These backups give you something to restore from if things go awry.
Now that everything is off and syncing is disabled, re-enable MobileMe sync on the primary Mac and set MobileMe sync to Manual. Turn on only Contacts, then click Advanced…
In the window which follows, select your primary Mac, then click Reset Sync Data…
The goal here is to push your best data to all devices. In most cases the best data is on the primary Mac, so in the Reset Sync window choose Replace Contacts On MobileMe with sync info from this computer.
If the MobileMe information was the best data to start with, reverse the sync direction during the reset and choose Replace Contacts On this computer with sync info from MobileMe. This is less common but sometimes necessary, such as when your iPhone or iPad had the best starting info.
The initial sync after reset can take several minutes to an hour. A glass of wine helps smooth out the stressful process of waiting with no visual feedback if all your data temporarily disappears (yep, that’s MobileMe).
Once the sync completes, check your info in both the Address Book and on the MobileMe website and make sure everything looks OK. Make a change to one entry on the Mac, choose Sync Now, then check that the change has appeared online. Once all is working repeat the process for Calendars.
If you have a second Mac, now re-enable sync on that machine in Manual mode. Re-enable Contacts, click Advanced…, then Reset Sync Data… The direction should be replace data On This Computer with Sync Info from MobileMe. This propagates good data from the cloud to the second machine. Complete the process, verify things are working, then repeat for Calendars.
On iPhones and iPads, go back to Settings –> Mail… –> MobileMe and re-enable the items previously turned off. When prompted choose Merge with MobileMe. It may take several minutes to an hour for all your data to propagate and resync, particularly for big calendars and thousands of contacts.
The Nuclear Options: Reset Sync Services, Delete iOS Accounts
When these methods don’t work, or if a system still won’t connect with MobileMe, a few remaining options. On Macs there is a hidden preference to Reset Sync Services. Option-Click on the MobileMe Sync icon in the Mac menubar and choose Reset Sync Services… This performs a reset of Mac OS X sync internals (caches, settings, etc.), to get systems communicating again. It does not merge or fix data content problems.
If that still doesn’t fix things, there are UNIX commands noted in this Apple Tech Note that you can enter into Terminal to get the job done. These have worked for me on occasion.
On iPhones and iPads, delete and recreate your MobileMe account to do a full reset. Go to Settings –> Mail, Contacts, Calendars and select your MobileMe account. Tap Edit, and then Delete Account. Return to the home screen, reboot your iPhone or iPad, then add a new account of type MobileMe. This replaces all data and resets sync back to square one.