ATT Read everything before excuting: I have found that Photos Sync in iTunes causes major problems (Error-50) when I try to sync my iPhone in iTunes. I un-synced the photos and everything else Syncs great.
The problem evolves from photos not associated or taken with iPhones I believe. (Cannon, Net, etc...)
I'm still working on this however, when I use iPhoto Sharing, (Not iTunes) I'm able to bring pictures back to my iPhone. I have found that one of the causes is from drag and drop from the Net. (Screen Wallpaper etc...) These photos can cause a world of issues because of the format.
These pictures can be changed to other formats and may stop this issue. (unproven)
I've also found that my backups have all been contaminated from these pictures. So, I had to go into Perferences in iTunes to erase all my back ups. Att: This may not be needed. Take care before erasing back ups.
This is still a work in process so, tread lightly. However, un-syncing Photos will get you a step closer, and stop the (Error -50) Any input would be great.