lua-gd png problem im:png

Hello there.
Tried to run example test/test2.lua for luagd library.
It seems there is some problem with im:png function - it returns true, yet no image is being written.
Tried to load png image and seemed to work alright. But writing png is not working for me.
I've checked that there is libpng13.dll present in clib directory.
What might be the problem? I have no idea how to fix this.
