Just a quick one, I had this on one of our ASA firewalls, post swapping out its PSU.
Its a lovely error as it just sits there and does nothing. You cannot get into RONMON as this is the first message that pops up on boot.
After a bit of playing I found that one of my RAM chips was causing the ASA to stop, when removed it booted fine. Reseating the RAM again and all was well.
Simple answer to an odd error.
Hope this helps someone else in the future.