Same thing just happened to me. I have a Dell Venue 8.1 Pro - windows updates complete, but did a Chipset update and now I'm getting the Secure Booth Violation. I managed to turn it off and reboot the tablet and had to use the BitLocker recovery key.
I got the tablet restarted after that and re-did the Chipset install to make sure it was successful then went back into the BIOS and enabled the Secure Boot option only to be faced with the same Secure Boot Violation message. Back into the BIOS turned off Secure boot and then was faced with the BitLocker key setup again.
I tried uninstalling the updates, but that action failed. Machine said it encountered an error and was unable to restore. That's the second machine I've seen the restore point error in this month.
Sooo, is it a windows update that caused it, or is there something else going on?