Sync error message on iPad, no message on iTunes
I have a very similar problem and an active incident at Apple Support: Error message on the iPad with no error on iTunes, connected via cable, not wifi.
The problem occurs for me when I have "Include Videos" in the Photos tab ("101 files could not be synced, check iTunes", but iTunes has no error: it just quit syncing after 77 of 178 videos). I suggest you change the sync settings on iTunes for Photos: Select all events/faces/albums but uncheck Videos/Movies, to see if it is the same problem. If you are not syncing from iPhoto but are syncing from a regular file system, there may be similar options. You should be able to determine what kind of media is not syncing via elimination with a bit of effort.
I have 19000 photos/videos (over 19GB) being synced from my iPhoto library to my iPad, and have narrowed it down to videos after syncing 1 year of my library at a time in several steps. Today I am working with the iPhoto support person to repair or refresh stuff in my iPhoto library so see if this helps.
Regarding IOS 5 and iTunes, however, the sync problem is not generating error messages to help find the problem and it has taken me hours of fussing and 3 calls to Apple Support so far to find out what is wrong (all via a process of elimination, not any diagnostic data or messages).
I had no sync problems at all before upgrading to IOS 5, the latest iTunes and latest iPhote 9.2
I will post the results of the Support incident once this is solved.