Please take each of the following steps that you haven't already tried. Stop when the problem is resolved. Back up all data before making any changes.
1. Turn off and restart the mobile device.
2. If the device is connected via USB, connect it to a built-in port on the computer, not to a hub. If it's already connected to a built-in port, try a different one. Also try a different cable, if you have one. You can also try to sync over Wi-Fi.
3. Delete the iPod Photo Cache. Quit and relaunch iTunes.
4. Check the names of all albums and slideshows in iPhoto. The names should contain only plain letters and digits, not any punctuation marks or other characters. Rename them if necessary.
5. Remove the soundtrack from any iPhoto slideshows that have one. If sync now works, you may be able to restore the soundtracks.
6. Repair or rebuild the iPhoto library. Be sure to back it up first.