Hi, I had the same problem as you, I got the answer from this website http://forums.mydigitallife.info/archive/index.php/t-23464.html
from the command line, i ran "afudos myfile.rom /x". this bypassed the romid check and successfully updated the bios.
it appears that afudos was looking in the wrong location inside the romfile on the disk for the ROMID. afudos still reports the romid is P4M800PR after the bios update.