Do a Software/Network Reset just to clear any cached data that may be causing an issue via
Machine Status > Tools > Troubleshooting > Resets > Software Reset > All Software > Reset.
After it boots back up give it another go.
If no change, machine Status > Tools > Security Settings > Image Overwrite Security > Disk Overwrite Now > Overwrite now
20-40 minutes later give it another go.
If no change,try disabling the authentication,reboot, then re-enabling.
If no change, Unplug the NIC and try to log in, obviously it fails, plug it back in and try again.
If no change, try updating the firmware (No idea here, just throwing ideas at the wall)