OK, I looked up that error and it basically says (translated) that ipxe could not configure the interface (i.e. acquire an IP address).
Following along with Tom’s post.
Is your dhcp server located on vlan 71 or is it on a different vlan?
If no, did you setup the dhcp-relay/dhcp-helper for forward dhcp requests from this vlan to your main dhcp server?
Does your dhcp server have a scope setup for this vlan?
If you plug a physical computer into this vlan does it pxe boot OK?
Did you setup vlan 71 specifically for FOG (i.e. is this a new VLAN configuration or has it been working for a while)?
Wait, thinking about this, you pxe booted so dhcp IS working because you are in the ipxe console already. If you press the s key at the above error message it should drop you to a console prompt. keying in dhcp should start the dhcp acquisition process again. If this was a physical machine I would suspect spanning tree here.