Originally Posted by davidfor
If you have only put one new book onto the device, you know it is bad. But if you put a lot on together, or still have some from earlier that have not been processed, you have to go through them by trial and error until you find the one causing the problem. The only thing you can do is go through the files on the device when it is connected to the PC and remove those that are not shown in the library on the device. Then put them back on the device one at a time, disconnect the device and see if it is added to the library. If it isn't you have the bad book and can probably add the others safely. But, do those a few at a time in case there are more problems.
Do we know the order in which the files are processed? I would say alphabetically by file name, which is easy to check from the files that have already been processed. It should then be trivial to identify the next one in line and try again without it.
If that can help sort (pun intended) things out faster...