I've a similar issue, but the story behind is different.
I recently moved to LMCE 7.10, and I have a MD that used to pxe boot fine with 7.04.
After moving to 7.10 the initial configuration went ok and MD was still able to pxe boot.
I decided to rebuild MD image after some glitches with video driver, and after this MD won't pxe boot anymore.
I get exactly to the same point as Coley, i.e mount call failed: 13
At this point I don't think that this could be a Unrecognized NIC problem, because if that is the case it should be appearing from the beginning.
Googling around I've found that "13" has to do with permission problems, because maybe client is trying to mount something that has not been exported, but when issuing a showmount -e on core it seems that everything is ok.
Is there anyone that have a better idea?
TIA and regards