There are a few things here.
Upgrade to 1.5.2 because it addresses a few issues.
The 780s did have an issue with pxe booting and picking up an IP address. I don’t feel that is the issue here, but just be aware.
Can you post a clean picture of the actual error so we can see the context of the error?
When pxe booting happens and then we see random issues with dhcp, that is typically related to having a network switch with spanning tree enabled (a good thing), but the switch is not using one of the fast spanning tree protocols (not such a good thing). As Wayne said, put an unmanaged (dumb) switch between the building switch and the pxe booting computer. If the computer boots and runs through FOG OK, then your building switch does have STP enabled instead of RSTP or what ever your switch vendor calls it.