I have to agree that this is something INSIDE of Windows Setup/Sysprep.
The customer I support just introduced a new model into their environment. This model experiences the same problems with the unattend file on an inconsistent basis ONLY on this model. Every previous model and all their OTHER current models have yet to exhibit this issue. The only changes made to the image were the inclusion of the model's drivers. Nothing inside the unattend.xml was/had to be changed, yet suddenly, failures.
This new device is their first to have SSD hard drives. It seemed at one point the customer's version of GHOST could have been the culprit, as it did not claim support for SSDs, but even after updating that to an appropriate version the errors continued.
This could ultimately be a driver or firmware issue, but in all of the testing, my device that I do my testing against has never produced this issue. The only other difference between my imaging and theirs is I DO lay the image down VIA provisioning, but the task is basically calling ghost to lay the image down and then rebooting. My provisioning environment uses the Windows 8 PE, where the customer's boot disc are VISTA based, as far as I can tell. I can't see where this would make a huge difference since the only thing being done with them is applying a GHOST image and rebooting into Windows Setup.