I have checked the application and based on the information I have found on its interface, I can say that the SHN files are compatible and ready to be converted to WAV format. You can see that in the image attached below. Make sure to run the software as Administrator if you plan to use it on Windows Vista or higher.
Additionally, you should check the SHN file that you attempt to add. It's possible you are trying to add a corrupted file.
