Why are our audio books stopping partway through?

We have lots of audio books and two IPods, a 120gb classic & a nano. Our audio books (abs) stop at the same minute & second on both devices - ie 5 minutes 33 seconds for instance - and won't play any further. Can't fast forward, can restart but always stops at same point. We'get tried reinstalling all music and abs after rebooting both iPods.

Can anyone help please?