I just updated to iOS 4.3 on my iPhone, which is connected to a MacBook Pro, and when the installation was done, tried to sync. The sync stalled at step four of four on syncing photos, with a message telling me that the sync could not complete because “The required file cannot be found.”
I called Apple right away, and the support rep, after checking with a few higher levels of tech support, asked me to uncheck the box to sync photos. The sync worked. I was then told that the problem had to be with one of the photos in my iPhoto library and that I would have to find it using the process of elimination. This didn’t sound like fun since I have over 3600 photos and this would take quite a long time to accomplish.
I tried to find a simpler solution and found it. Incorrectly thinking that it might be in the last import, I had my iPhone 3GS sync all events except the last one. The sync worked flawlessly. Then I added the last event and the sync still worked. Next I added all the albums and faces, and the sync worked again. I girded my loins and decided to try to sync all photos, events and faces … and was able to sync perfectly.
My iPad had the same issue, but first unchecking syncing and then re-syncing everything (which took a while, as all of the photos were re-optimized and copied over) worked just fine. So, at least for me, there was a problem with syncing photos, and in both cases deleting the photos and then having the computers and iDevices sync all photos, events and faces solved the problem.
I don’t know how widespread this problem might be, or if it even affected anyone but me, but if you are in the same boat, give this a try.