The filesystem might have been corrupted when the microsd went bad. First, back up everything on the Express. Then format it (Settings->Format), reload the files, and try again. If that doesn’t do the trick, try a reset (Settings->Reset).
BTW, the Clip+ is much nicer than the Express for resuming in audiobooks and such. They just don’t do so well in the washing machine so I’m stuck with my Express for a bit. 
