It is possible to downgrade the BIOS version of the NUC. You just need to download the prior BIOS version from our website and run a BIOS recovery. It is necessary to use a USB drive plus remove the BIOS configuration jumper.
According to the error, it seems a BIOS setting is causing the error. I suggest you to get into the BIOS and reset settings to default.
Be sure your memories are DDR3L-1333/1600MHz at 1.35V SO-DIMM.