Netinstall -PXE issues

Long story short - I have an RB 112, bootload 2.18 - and have unfortunately reset the whole thing after a failed upgrade to 3.28.

I’m trying to use NetInstall as per the Wiki, but it isn’t seeing my Altiris PXE server, so NetInstall doesn’t see it.

I am getting the following:

Press any key within 9 seconds to enter setup…
kernel not found
trying dhcp protocol… OK
failed to resolve mac address
kernel loading failed

Is there a particular port that it needs to bind to? Have I overlooked something in the PXE setup?

Altiris is running on Windows Server 2008R2, DHCP is running and I have FreeDos as the PXE image to push out, using DHCP option 60

Should I try bootp? Are there any good guides for bootp?