My D800 was freezing up before and after the firmware upgrade. I upped the speed to 800x on my Lexar cards and I haven't had problem with them. Could this me the issue? Oh I hope so. There is nothing worse then having to take your battery of the camera and put ti back in to get it to work again right in front of a client. So far it's only happened on portrait sessions. I would freak if happened at a wedding or bar mitzvah.