If you are loading large files you might get this if there isn't enough usable memory.
For ''pcbios'' boot the memory is especially limited in different ways, even if there is magnitudes more RAM installed in the machine, see [[http://forum.ipxe.org/showthread.php?tid=11991]] and [[http://lists.ipxe.org/pipermail/ipxe-devel/2016-March/004793.html]]