Hi, I have been having problems today exporting sprite sheets as well. It has always worked in the past but now when I save them, there is nothing there, no file at all. The png files I have been using are 96x128 pixels so I don't think there is a size issue. It doesn't even save each frame as separate png files. I've even used an old animation that I've used to make sprite sheets with in the past and that does not work.
I'm taking part in this weekends Ludum Dare, hopefully I can figure out a solution in time.