I've been using unraid 6.6.7 pro for weeks now. I did a clean shut down a few days ago and when I powered back on I received an error after selecting either the local GUI or GUI safe mode.  See picture for error. The usb I am using is new kingston. After loading a trial version of unraid on a different new kingston. I was able to load the GUI without issues. I can see all the files on my original USB (key, etc.) but do not have a backup or a way to boot into the GUI to create a backup.