Q: What does message "iTunes was unable to load data class information from Sync Services.  Reconnect or try again later." mean?

I am also having the dreaded "iTunes was unable to load data class information from sync services." message.  It seems this issue penalizes anyone who HAS updated all of their computers with the latest updates.

I have tried all of the common fixes listed but have stopped short of a full system restore.

Anyone else have any luck with the technical support people?

It doesn't correct it with a full system restore I've tried that also?

Apple also appear to have pulled the 11.3.1 release of iTunes, trying to find a copy of that before the .2 spot release to see if things magically come back to life.

But considering the number of people who MUST be affected by this, their silence is deafening.

My iphones 4 and 5 doesn't sync I have two ipad ones that I use just for music, and a ipad air, and none of them will sync, but the only thing that will sync is an old 7 year old ipod ? doesn't make sense

Previous versions of iTunes are available here, http://betdownload.com/itunes-19-download/11.3.0.54-64bit-version.

I'm trying the 11.2.1 release.. failing that i'll uninstall and go back further until Apple sort this out.

But initial attempts look futile... might need to uninstall all Apple products and start again as it looks like the sync server has been totally knackered by the 11.3.1.2 release.... NICE ONE APPLE!!!!!

Just so people don't waste there time I spent four hours last night trying to solve this by uninstalling all the apple software, cleaning the registry completely with any Apple wording, removed Office 2013, disabling all virus and firewall protection, stopping syncing services and then ran CCleaner again to make sure its all gone. The problem still exists after iTunes reinstall. It is stopping both my iPhone 5s and iPad Air from syncing.

Tried with a completely new user and new iTunes database, the problem is still there.

Downgraded the iTunes version to 11.2 and the issue is still there.

Linked my iPad and iPhone to another PC and they sync fine so it is not the devices.

I think there are two options wait for a fix from Apple, or completely trash the PC and reinstall Windows 8.1 from scratch and then install older version of iTunes on the fresh install.

What a waste of time

Having exactly the same problem. Spent 3 days trying fix this nightmare. Nearly clobbered my Windows 8.1 PC by doing umpteen system restores. Almost was going to install Windows 7 and do a full update of PC until I came to this thread. Was on phone with Apple support in Ireland who have taken log files and msconfig files.

Irish tech support were superb but had no solution so its obvious this problem has sucker punched Apple Dev HQ as there are no obvious and immediate fixes.

Do we just have to play the waiting game then? I have lost the motivation to continually try different unsuccessful fixes! It has not been a fun couple of days.

I'm running a business and manually keeping Outlook / I-pad / I-phone aligned is not what I need.  If problem is not sorted by tomorrow I will be taking necessary steps to migrate to Samsung products.

Try asandhu3's solution:

"iTunes was unable to load data class information from Sync Services" error?

I'm having a go now as it seems to work for many people.

I have tried asandhu3's solution but as this was a fix in 2012 and has nothing to do with the recent windows updates and the recent release of iTunes, it does not work at all.

"iTunes was unable to load data class information from Sync Services" error?

Yep, you're right. Thought it was too easy

Had exactly the same issue - have backed up on different computer ok, but tried original again and no joy!!

This problem seems to be caused by Microsoft update
KB2822241 on 18th August, and I think only effects host PC’s that
are connected to Microsoft Server.

As stated by others, system restore doesn’t uninstall the critical update,

and the Microsoft updates today the 21th doesn’t fix it either.

Isn't that a Win 8 only update?