I had a similiar reboot issue after upgrading to the latest OS on my 8100. I did the media card fix of copying everything off the card onto my hard drive and reformatting the card in my BB. I deleted all the thumb files or whatever they were called from the music/pictures directories and added all of my stuff back onto the fresh formatted card using mass storage option. Well, it hosed again. I reformatted and added folders back one at a time and it seems that music, voice notes, video etc. was fine but there is a picture in my pictures directory that my BB does not like. I left that folder off till I can add them a few at a time to narrow down which one is hosing it up. Those BB thumb files need to be deleted from what I understand but I still have a picture taken with the old OS that is hosing up my media card.
I would add things back a few at a time to narrow down the culprit.
Good luck with it,