[Toxaris]

You can ignore PNGOUT. It is an old leftover I apparently forgot to delete. The reason I kicked it out, is that there is no Linux/OSX version and it is closed source (no way to rebuild if the need arises).
The program is checking what the OS is to determine how to call the image optimizing programs. If I recall correctly (will look it up later today), on Windows systems it will use the executables in the directory and for Linux (and also OSX) it should use the ones in the path. Based on your error report, it seems that it does not starts fine, it tries to open 'open'. I will get back to you.