My SANA express also started giving me BOOT Error, SHUTTING DOWN messages. It would start building the database, the yellow battery icon would appear on the left of the screen (as opposed to the right) and then the boot error message would appear and the device turn itself off.
I followed the link, and then the instructions to update the firmware but did not have any success.
Finally out of desperation I moved all the files from the root directory of the device to my local pc, leaving the music, playlists, and record folders as the only things on the sansa drive and then ran the firmware updater. It did not rebuild any of the files in the root folder or delete any of my music files. I then removed the hardware from my windows XP machine.
I turned on the Sansa and after the device rebuilt the database without an error it was ready to play music again.
When I plugged the device back into my laptop, I could see that the files I had removed had been rebuilt, so I’m guessing it was some type of database or file corruption causing the issue.