If there is anyone present who wants to upgrade the flash, let them speak now,
or forever hold their peace...
IIRC, this part is from the (usually) non-upgradeable part of flash. If it's not managing to run to this point consistently, then I suspect that your flash chip (or something else worse) is hosed somehow.
Couldn't lockdown flash (ram fault?)
...which is sort of implied by this.
And the "hold their peace" part
is the prompt to the serial upgrader, so in case I
am wrong, it might be worth persevering a few times with the upgrader, in case it does get to this point and then successfully reflash.