I've had this XPS 8900 for a little over a year and just started getting error on startup. A message appears in upper left hand corner of black screen during boot up. Unfortunately, it doesn't stay active long enough to capture all of the message. However, I do know that some failure is reported and the message includes ME Firmware Downgraded or something very similar.
I saw the thread earlier but questioned the recommendations. It seems that the solutions presented had mixed results. Also, when a second hard drive was installed and Dell helped me set it up for RAID-1 (Mirrored Hard Drives), Boot Mode BIOS settings had to be changed in order to complete the setup. However, it should be noted that the RAID-1 setup was done a year ago and I did not experience the ME Firmware Downgrade error until yesterday nor have I changed BIOS settings since the RAID setup.
It just seems prudent to look into the problem in a little more detail. Having said that, it would be nice to get a good explanation of just what "ME Firmware Downgrade" and "Request MeSpiLock Failed" really means.
The ME stands for INTEL MANAGEMENT ENGINE.
SPI lock has to do with failed bios update and internal MANANGEMENT ENGINE FIRMWARE.