This message appears after the system drivers are loaded. The BIOS setting can be changed from UEFI to BIOS and saved with no error but when you go back in and check it UEFI has been selected again. It cannot be changed.

I have so far removed the BIOS IC (25Q128FV), erased it and reprogrammed it with a known working BIOS but this did not solve the problem. I then erased the iDRAC SPI chip and again reprogrammed it with known working firmware, repurposed the system using the SDcard and firmimg.d7 but the problem persists.

Having updated the firmware, drivers, iDRAC, BIOS and Diags the system boots OK, iDRAC fine all except for the FVS mode is still enabled.

At least I can say I know what isn't causing the problem and it's not the obvious. I have even tried with the bare minimum hardware ie one PSU, one CPU, no HDD's, no RAID controller and no network card.