panic: free: guard1 fail

i'm trying to do something which maybe can't be done, so I'm not surprise I got the above error..

I would like to boot FreeBSD via PXE using FreeBSD 11.0-RELEASE bootonly iso... To my surprise BTX loader starts up and then the bootstrap loader starts, before:-

FreeBSD/x86 bootstrap loader, Revision 1.1
(, Fri Mar 25 03:48:09 UTC 2016)
panic: free: guard1 fail @ 0x63722736 from /usr/src/sys/boot/libstand32/../../../lib/libstand/ufs.c:689
--> Press a key on the console to reboot <--

I have no idea what this means, but wondered if there is anything I could do to get around this...

I did manage to get this to work with an old version of FreeBSD, possibly 8.0, but no newer versions.

I am aware of mfsBSD, but always seem to have problems trying to get it to work