RN 104 won't run backup & locks up after 6.4.1 update

I didn't make it clear in my original note that I used chkdsk, but I did mention that I had checked the USB volumn and found no errors (but I did use chkdsk to do that) I also safely ejected the USB disk before plugging it back into the ReadyNAS and attempting to run the backup. I have now followed this same procedure 6 times to attempt to run backup and every time it starts the backup and locks up (it won't complete the backup, it continually flashes the backup light, it locks up the backup utility and claims I don't have any backups set up on the readynas, it locks up the backup log and claims there are no backup logs on the readynas, and it locks up the other system logs and claims there are no system logs on the readynas). When this happens I also cannot shut the readynas down (I have to unplug the USB drive from the readynas before the readynas can be rebooted or shut down (and of course this leaves the USB drive in an unstable state so I have to run chkdsk on it, safely eject it and reinsert it into the readynas port. After rebooting the readynas I then can see my backup job,  I can check both the system logs and the backup logs and they indicate the backups have all lasted less than a second and the USB drive is read only.

I have successfully copied files from the readynas manually to the USB just before I run the backup so I know the drive is not read only before the backup job starts. It's the backup job that is causing it to become read only.