Here is the working USB stick thread. Pretty long list of what usually work and what to avoid.
http://forum.doozan.com/read.php?2,1915
IMO, it's partly in the U-Boot version that you're running. Usually it handles typical USB thumb drives very well. But some thumb drives are of low quality (e.g. Patriot), and it will fail to boot.
http://forum.doozan.com/read.php?2,1915
IMO, it's partly in the U-Boot version that you're running. Usually it handles typical USB thumb drives very well. But some thumb drives are of low quality (e.g. Patriot), and it will fail to boot.