Sometimes updating the firmware will make the player revert back to ‘defualt’ settings. This means that your player’s USB mode might have been switched back either to MTP or Auto-Detect. It is easier to connect in MSC mode.
I would first follow blackdog’s suggestion to switch it to MSC mode. Or as a last resort, you can go back to the previous firmware. You’ll have to do it manually as the Sansa Updater will not ‘back-date’.
Here’s a link to the previous firmware along with instructions on manually installing it.
