At a guess I would say that you are saving the files in the png format as that script uses SaveForWeb to export png8 or png24 files. All other formats are saved using the normal document.saveAs method.
If so you need to check your output settings under the fly-out menu in the saveForWeb dialog. Look under Saving Files and make sure Unix is not checked in the Filename Compatibility section. That is not something the script can control. With Unix checked SFW replaces spaces with the - char.