I think I see what the problem is. You need to upload the PostReplace folder and its contents into the Library folder.
@Kier@Mike@Brogan I've just checked the zip file and it just contains a PostReplace folder and a _MACOSX folder. If it contained a Library folder with the PostReplace folder inside as per other add-ons then it would avoid any confusion about uploading. Maybe it should be repackaged?