Duo x/2 chip

[sevi]

Hi guys, Hope someone can help with this one. I've just started installing these Duo x/2 chips that have a dual bios setup on them. This is the first time I have dealt with these as I was installing Aladdins beforehand. Anyway, the install went sweet, the chip fired up (pre-loaded with x2 4979 bios on bank 0) and successfully formatted and loaded evox with my install disc. However, when I tried to flash the x2 4981 bios from my install disc the xbox froze just as the word "erasing" appeared.
If anyone is familiar with these chips can you tell me if I have to hold the power button down for a certain amount of time to make the flash writeable?
Any help is, as always, much appreciated.
Cheers.