iphone could not be synced because the sync session failed to start

The current version of iTunes at the time of posting is 12.6.2.20. If you really are running Windows 7 and Apple Software Update isn't fetching the new build for some reason then download a fresh copy from iTunes - Download iTunes Now - Apple, and ignore the paragraphs below. If you have any problems with the update see Troubleshooting issues with iTunes for Windows updates.

If you run Windows XP SP 3 or Vista then iTunes is maxed out at version 12.1.3.6. (which is why I question which version of Windows you have). While it seems users with iOS 10.0 through 10.1 were able to sync and backup with this older version of iTunes, upgrading or restoring a device running iOS 10 requires iTunes 12.5.1 or later. It would also seem that iOS 10.2 broke the ability to sync with iTunes 12.1.3.6 and the minimum version for iOS 10.2 is iTunes 12.5.4.42. You can backup to iCloud.

Upgrading to Windows 7 or later would let you install the current version of iTunes, or see Move your iTunes library to a new computer if you decide it it is time for new hardware. Alternatively you could take out a subscription to iTunes Match which would allow music added to your iCloud Music Library on your computer to become available to stream or download to your device. See Subscribe to iTunes Match - Apple Support for details.

See also Import photos and videos from your iPhone, iPad, or iPod touch - Apple Support. If you unlock your device before connecting to your computer it may still register as a digital camera type device, allowing you to copy off any photos. Otherwise iCloud and Photo Stream may work, or you can use email, Dropbox, or similar tools.

tt2

Just made one very simple move without having to restore iPhone or reinstall iTunes.. 🙂

1st step:http://support.apple.com/kb/TS1538 *Read 'in my case' in here first before following this link*
Follow that link to restart (or if necessary) reinstall your Apple mobile device support.

In my case, Leave iPhone connected all the way. I first exit iTunes. Then i stopped the Apple Mobile device support (by following a part on that link above in step 1) which Effectively made my iPhone undetectable on itunes but discoverable by windows as a 'camera device'. Then while device is still connected, i started the Apple mobile dev support again. Now i open itunes and there my iPhone re-appears.

2nd step: After your iphone re-appears on iTunes, press Sync and all is well... 😉

P.S, Mine is iPhone 4 running on iOS 5, iTunes 10.5, Windows 7..

If, by chance you are running windows 7 or Vista, try starting itunes as an administrator. I had the same problem, solve by running itunes as administrator. I respect Apple, however this lack of attention to detail is very out of character. Is all character dead?

All I did was exit itunes and open it again. It began syncing automatically. Whew.

Exiting iTunes, without disconnecting or ejecting the iPhone, and relaunched the iTunes application fixed syncing. I had tried ejecting then reattaching the cable, restarting the computer, soft reboot on the phone, etc...

This solved my problem, too. Thanks!

This solved my problem too: I just quit iTunes and relaunched, sync started successfully on iTunes start up. (OSX 10.68)

I'm running a mac with my 3gs iphone with 5.01...

The sync starts then hangs on step 6 of 7 "determing tracks to sync"... any thoughts?

This solved my problem as well.

Worked for me too.

i tried this and everything i could find in other support communities, but nothing seemed to work. checked some settings and realized that my default location to store music had been chnaged (maybe during an upgrade?). so my music was being stored in two different folders. changed my default back to the one location i wanted and moved everything that was in the other folder back to this location, helped itunes find the songs, sync'd...everything works fine now. it worked for me.

iphone 4 with latest software

latest version of itunes

windows xp

I left the phone plugged into the PC with the sync cable, then I exited iTunes. I then went to device manager, found "Apple Phone" listed under portable devices and disabled it. I reopened iTunes and the sync process started (and finished). I went back to device manager and enabled Apple Phone.

Worked like a charm!

iPhone 4 running iOS 5.0.1

PC running Windows 7 Home Premium 64 bit

iTunes version 10.5.1

exit itunes without unplugging and then open itunes again. if this doesnt work, uncheck apps & photos, sync again, before finish syncing stop it, then check it again.

just upgraded from 4xx to 5.0.1 and saw this - worked for me too, exiting and restarting itunes (leaving phone plugged in to my Mac). thanks!

Like ArrrJay - I'm running Vista and had to run iTunes as an administrator (right click on the shortcut and select "run as administrator")