The BeagleBoard xM rev C board requires the following change: http://git.denx.de/?p=u-boot.git;a=commitdiff;h=f6e593bb1255d1e15201cb5dec8c95264489e729 Which is already upstream and should be included in the 2011.06 release due out soon.
Updating now
http://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=0d029ba065be7242f110db4a7303b3cb465318ac