I'm having the same "Sync Cancelled" problem on my iPod after i installed iOS5.
I just found an Apple support article that may help, though I haven't tried it yet;
I tried that fix suggested by Apple for spontaneously cancelled sync, but it failed to solve the problem. Sync continues to cancel itself without finishing.
I have about 12,000 photos syncing. Sync counts down the photo syncing on Step 6, then always eventually stalls on one, and then cancels without finishing. I never had any syncing issue with any iOS prior to iOS5.
If someone has a solution, please let us know.
I am having similar problems, I try to synch my ipad and it keeps 'cancelling sync' right at the end. As a result, I can't transfer any purchases I've made on the iPad to the computer so if I restore the ipad, I'll lose these.
Although hearing others talk about this problem, it doesn't sound like a restore works.
Please help Apple, or you will find one new ipad 2 dumped back on your doorstep.
I fixed my issue with syncing locking up on my iPod 4G. I found that large format MOV files in synced photo folders stopped my sync. It's ironic that my problem was only caused by Apple's own video container format since MPG and MP4 files did not cause the problem.
It's great that IOS5 now transfers some videos along with the photos so that one can view videos in photo slide shows (something available in GraphicConverter for years now). Through trial and error with my iPod, I've found the following issues and fixes with syncing videos in photo folders.
Since many .MOV video files in a synced photo folder will stop the sync, I found that they work if converted to VGA size (640x480) MP4 or M4V iPod files, which will sync and play just fine on the iPod. (Most MOV files can be converted Quicktime 7 Player export to MP4 or M4V.)
However, I found that large format MP4 files (e.g. HD 720 or 1080) are not copied, but don't stop the sync on my iPod like the large MOV files did. They are just ignored by the sync and counted in the sync error count message that appears on the iPod at the conclusion of a sync.
Hope this helps.
Here's how I solved my problem about cancelling while syncing.
It always cancelled while I tried to sync the entire library.
So I tried to sync from the artist list, one at a time.
Until I find the one that cause the cancellation.
It appears that the song is corrupt. The weird thing about that song is that it won't sync on my iPod, but works fine on my other iOS devices.
I delete the song.