I've been fighting this losing battle for days now. I'm currently running 5.00 m33-4 on a PSP slim (Even tried with 6, but got the same result.) When I run the upgrader, it gets to 92%, then gives me the error code FFFFFFFE. This is around the time my UMD drive starts trying to read for a disk (Though the laser is shot, so no go there.) One time I did try opening the drive door, it stopped trying to read air, and the upgrader made it to 99%, then it would sit there for a minute and go back down to 84%, and repeated for a good hour before I called it bricked and restarted.
Any help is greatly appreciated, thanks.