PXE boot - NBP is too big to fit into free base memory

I'm afraid your network hardware doesn't support boot images of that size, try to reduce your boot image or make it a two steps loader.

There's a good guide on the gPXE wiki about chanining gPXE into a 2 steps boot, have a look here

Max size that you can load as first stage boot code is 640KB and that is if no space has already been used.

I think the issue here is that you try to boot the iso directly, instead you need the boot NBP part only. In the more modern iPXE (based on gPXE) the filename would be ipxe.pxe or undionly.kpxe depending on what NIC you have and what you want to have support for in your PXE environment.