Q: The iPhone "..." could not be synced because the sync session failed to start

Would you happened to have upgraded to Itunes 10.5b as a developer?  The same exact message appears for me and I did just that.  I ask because the installation became available today (Jun 24, 2011).

I found that to be the solution as well.  My iPhone is running the IOS 5.0 beta 2 and is syncing with iTunes 10.5 beta 2 right now!

iTunes

The version of iTunes that comes with beta 2 cannot sync devices that have the beta 1 software installed. To avoid this problem, do the following:

1. Sync any devices that have beta 1 installed to the version of iTunes that came with beta 1.
2. Upgrade iTunes to the version that comes with beta 2.
3. Connect the device and install the beta 2 software. (Understand that you might see a failure to sync error when you first connect the device.)
4. After installing the beta 2 software, restore from your the backup you made in step 1.

I installed the new iTunes beta before I tried to upgrade the new iOS beta. I'm getting the yellow "other" bar. I tried reverting to 10.5 beta 1 but it won't launch. I realize I could upgrade to iOS 5 beta 2, but I need to back up first. Is there any way I could force a backup, or am I totally screwed here?

You can fix it. Delete (trash) your new iTunes install, empty the trash, then reinstall 10.5 beta 1. Something in the App package doesn't get overwritten unless you trash it completely. I just did this on mine and was able to sync with 10.5 beta 1 and then upgrade to 10.5 beta 2.

That said, iTunes seems to think that June 8 was the last time I synced my phone, even though I sync every couple of days, so I still lost 2 weeks worth of data in my call logs and text history... :/

Agh, I followed all of the steps correctly the first time and I'm still getting this error! I have iOS5 beta 2 and iTunes beta 2 but they're not syncing!

The solution tho this problem in my case was to put the iphone in DFU mode and restore to the beta 2 of ios 5. After this the phone was able to sync with iTunes again and restoring from the backup was also possible.

Any hints where I can get a hold of beta1 again? Can only find download links for beta2 :-/

Where can I download the previous release of iTunes? I've updated iTunes before making a backup of my iPhone (stupid but :/).

metro6audio's post about deleting, trashing and emptying the trash for iTunes allowed be to go back to beta1 and backup before I move to beta2.

Thanks metro6audio!

Found it at https://developer.apple.com/devcenter/download.action?path=/ios/itunes_10.5_beta /itunes_10.5_beta__mac.dmg

deleting itunes doesn't work for me

i got itunes 10.5 beta 2 running on my macbook and iOS5 beta 2 on my iPhone, but can't sync because of this error ...