Same her, my Kingston card no longer works in my Express.
After I contacted Sandisk to explain my problem, their only solution was to send it back. I have two concerns with this; they will relace it with some refurbished clunker when I purchased a new product and the fact that accroding to them there is nothing wrong with it since this is a valid firmware upgrade. They seem to be trying to blame it on the memory card. Oh, and they state that my idea of reverting to the previous firmware version, if even possible, would damage the hardware.
Updates like this make me wonder if Sandisk thinks that they are the Microsoft of the MP3 player world. I cannot reccommend this player to anyone else even though I really liked it in the beginning. I am telling everyone I know not to buy one but if they do, to not even put the CD that comes with the player in their computer. Throw it out!
I have warned a friend about the firmware problem as he bought one shortly after me. I caught him in time. Please warn others as this latest firmware upgrade does nothing that I can see to improve the player, it only breaks existing features.