PXE not working for 1 type of system / PXE-E53: No boot filename received.

I'm having some issues with PXE and our HP DC7100 machines, for some reason
they all keep giving a PXE-E53: No boot filename received. error.
All our other workstations work fine with the imaging boot exept these
dc7100's.
This is somewhat of a problem considering they dont have a cd-rom or floppy.
pdhcp is running on the same server as the dhcp server, I have option 60 set
in dhcp.

-
Arjan