FreeNAS-9.1.0-RELEASE-x86, and I tried both winimage and Win32DiskImager to write the image to a usb stick. I tried the iso version which also gave me the same message when I written it to disc. When I tried PC-BSD it would not work either. I tried the same USB stick in a different computer with more updated hardware and it worked. The one it will not work in is a HP Pavillion a775c with a 32 bit cpu and 4 GB of DDR ram.
I did have a version of CentOS on it before, so puzzled with the message from FreeNAS and the other FreeBSD based distro. It seems to definitely be something to do with hardware and/or a bios setting.