It's just a guess since I came across both of these posts while searching for solutions to grub problems myself, but could this be what you need?
http://www.opensolaris.org/jive/thread.jspa?threadID=66519&tstart=0 ">>>>>>>>>> IMPORTANT <<<<<<<<<< Due to changes in the GRUB boot system, one must manually update the Master Boot Record (MBR) to include these latest changes. Failure to follow these instructions when updating from 2008.05 (build 86) to a later build will result in a system that does not boot by default and instead the original BE must be manually selected." This message posted from opensolaris.org
