BriChi,
Hope you get a response from Pioneer soon on this but I was just thinking about this issue and thought I share my thoughts...
If we think of the player as a computer or a drive, maybe the operating system or something on it is corrupt so maybe try calling tech support and see if there is a way for you to format the players.
Also on that note, have you tried reloading the firmware one more time? At this point, I can't see what harm it would do. Get a fresh copy and flash it again.
Good luck bud.