Iridium
I've flashed a lot of players and some many times (to test what the new skins look like) so the process of flashing is not a problem. It's
WHAT you flash it with is the issue.
Wrong or incompatible firmware = dead player 
I don't trust the firmware on the cd's. They are very generic. For obvious reasons, they save on cost if they just ship ONE cd for all different type of MP3 players they manufacturer. I got a cd with one of my players that has over 8 different firmwares on it! I don't dear to try them in case of incompatibility problems.