I was following http://barebox.org/documentation/barebox-2011.05.0/x86_bootloader.html
I am getting the error:
“No MBR signature found
barebox image seems not valid: Bad MBR signature”

At first I was trying it with OpenSuse and thought the problem could have been related to it being 64-bit, however I am also getting the error on a 32-bit build of Debian.

A hexdump of sdb does show “aa55” at the end of the 1st sector.