We got two machines, WC 7530 and WC 7830. Both were working, but after replacing the HDD because the real owner took it, we are having issue in upgrading the firmware. These are the things we did:
for WC 7830 HDD 121K56430
for WC 7530
As far as I know, there is no such possible security option.
Also, might as well be trying with the latest firmware instead of the General release since it will let you skip doing an upgrade later.
Easiest method for the file creation is via Notepad, File> Save as (Make sure it is on All files or you will get a txt extension added). Now you don't have to un-hide things and delete the TXT
With the Forced_UPGRADE and the DISABLE_DATA_BACKUP options added, I can't imagine what is happening , it implies something odd was done when they removed the drives, possibly the removed something else as well.
It can't be a glitch on 2 very different hardware/software platforms, but I can't think of what it would be either since they have tried 3 different USB sticks.
20 minutes is too short to wait for a full altboot though, I recently did a 75XX that took more than that to even begin, it was nearly an hour before completed to boot, and it had to reboot twice after that, I'd say it took a full hour beginning to end.
Oh, and here is the latest for the 75XX