So i figured it out. and it makes no sense to me..

Somehow a while ago (like 5 months) I must have made a typeo when creating my customzed initrd. (this was when I was fixing the broadcomm b44.ko driver to work)

The root of the minirt.gz had a file called ..miniroot

I found it by accident. Once I removed that file and re-created the pxe minirt.gz it worked fine.

I don't understand how just this one model of machine broke, or even why it broke. but it's fixed now.

chalk this up to PEBKAC