I think the problem lies in not having enough disk space in your iPad. It needs some fair amount of temporary disk space to complete the backup process. When it ran out of space, it just crashes.
The app that was causing my problem was FltPlan, which I had downloaded the maps of the flight plan in the cache (temporary storage). (When you download the entire map of the United States, it eats up a lot of disk space.) After I deleted the downloaded maps in the cache of FltPlan, iTunes backed it up without a glitch.
So the solution is: make some room in you iPad. Delete the temporary cache (if you are techie enough to do that). If not, just delete some apps. Don't worry, you won't lose them, because you can always reinstall the same deleted apps later from AppStore (because Apple has a record of all your purchased apps in iTunes/AppStore, and you can always reinstall them in any device you have - either iPad or iPhone or your Mac. You can easily find all your apps that were "purchased" but "not on this iPad" button in AppStore/iTunes and reinstall them later after you completed your backup).
If you delete the app first before backing it up, delete those apps that you don't have any saved document or saved settings, such as if it is an text editor and you have written notes in it, don't delete it, otherwise you will lose your notes. Same for games, if you have played the game and saved the level your are in, when you delete it, you will lose your scores. So delete those apps that you don't have any save data in it.
After you made some room in your iPad, then backup with iTunes.
I think Apple should give a warning telling you that it ran out of disk space to complete the backup. That will save some grief for everyone.
