[Unattended] M2N68-AM Plus cpu detection problem

I'm using unattended 4.8 to install windows XP using linux pxe booting,
and got a new batch of motherboards (Asus M2N68-AM Plus) that boot the
linux portion fine, but fail in windows setup saying:

Setup has determined that this computer does not contain an 80486 or
later CPU.  Windows XP cannot run on this computer.

There's a Athlon II x2 250 installed, which is considerably more recent
than a 486.  Any suggestions?


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