Ok, I found a way around when using ISOs that ZXBtools don't like:
1 - I do everything nornmally until it crashes, then kill the process
2 - I flush the directory of the game it crashed
3 - Using UltraISO, I extract the ISO to the directory
4 - If it crashed before the last game, I create the folders not created, e.g. Game3, Game4
5 - Using UltraISO again, I extract the games to go in the folders I just created that ZXBtools didn't do since it crashed
6 - When I finished, I use UltraISO again to build an XBOX ISO from the whole C:\temp1 directory
I then burn the ISO, delete the C:\Temp1 and zxbtools\XDVD directories, delete the files in zxbtools\Temp, and I'm ready for the next one.
It sucks, but at least I can make it to work. And it's still much faster than trying ZXBtools over and over again, having to start from scratch each time, and never getting an ISO done.