PXE boot problem using netboot.xyz "mounting tmpfs on /cdrom failed: Invalid argument"

I've set up my pfsense server with tftp to support PXE booting. I've configured it to boot the latest (as of posting) version of netboot.xyz. This works to a point, but I've tried loading a few Linux images and they all seem to die with the same error messages. Key output text includes: ... mount: mounting tmpfs on /cdrom failed: Invalid argument ... curl: (23) Failed writing body (0 != 16384) Unable to find a live file system on the network ... Screenshot: I'm not sure if this is a tftp issue (I doubt it), a pfsense issue (I doubt it), a netboot.xyz issue (my main guess) or something else.