Although Apple's iSync and MobileMe have worked well for some users, others have experienced problems ranging from data not syncing to an inability to access the calendar feature on the MobileMe web site. While Apple is working on fixes for the problems at hand, the guys at MacFixIt have posted the following guide to help fix problems as they arise:

-First, back up data to a safe location.In iCal, users can export their calendars to a safe location either by exporting individual calendars or backing up all of iCal in the File menu, and in Address Book users can export their contacts as a vCard or as an Address Book Archive.

-Once the data has been backed up, users should pick a central computer to be the initial source for the synchronization (all other computers and devices will have synced data wiped).

On all computers: Open the iSync application and reset sync history in the program's preferences.

Remove the following folders from the computer:
.../username/Library/Calendars/
.../username/Library/Application Support/Address Book/
.../username/Library/Application Support/iCal/
.../username/Library/Application Support/iSync/
.../username/Library/Application Support/SyncServices/

Open iCal and there should be the default calendars listed. Likewise, Address Book should be empty.

In the MobileMe preferences on one computer only, select only the "Calendar" and "Contacts" options, and again in the "Advanced" option select "Reset Sync Data", clicking the right arrow to replace all sync info on MobileMe with that on the computer.

Upon syncing, all data on MobileMe should be erased. Check online at www.me.com to ensure the addresses and calendar are cleared.

Open MobileMe system preferences on all computers and deselect all items.
Unregister all computers from MobileMe in the "Advanced" section.

Uncheck "Synchronize with MobileMe" and in the "Account" tab, sign out of MobileMe.

Clear the contacts and calendar from mobile devices, such as iPhones.

On the source computer:
Open iCal and from the File menu select the option to reimport the calendar data. If users exported individual calendars, then the "import" option should be used, and if users backed up their whole iCal calendar then "Restore iCal" should be used.

Do the same with Address Book so all contacts are now available there.

Open the MobileMe system preferences and sign in with the MobileMe account username and password. Then select the items to synchronize in the Sync tab and click the "Advanced" button.

Click the "Reset Sync Data" option (again) and again replace all data on MobileMe with that from the computer by selecting the RIGHT arrow.

Check online at www.me.com to ensure the calendar and contacts data has been synchronized with MobileMe.

At this point, users should now test synchronization by creating a small change such as a new calendar event and see if it propagates to MobileMe without any errors. If the test works, propagate the data to other systems and send the new data to the other computers and devices that you're working with.

If you've seen these syncing errors on your own end or discovered fixes or workarounds for them, let us know over in the comments or forums.