PNG2WAD successfully creates WADS from the example PNGs, but I haven't gotten other PNGS to work (contains no map data).
This includes if I load one of the example PNGs into Paint.net then save it again without making any changes.
Does the PNG have to have a specific bit depth (paint.net is set to automatically detect this)
Edit: I set the bit depth to 32, and it works fine now.