There were errors with Info.plist checker, which means App Wrapper doesn't know the name of the icon file.
Select "Information Property List" from the "Edit" menu and manually add a string entry using "CFBundleIconFile" as the key, and a value like "AppIcon". Make sure the icon file is called "AppIcon.icns".
Select "Information Property List" from the "Edit" menu and manually add a string entry using "CFBundleIconFile" as the key, and a value like "AppIcon". Make sure the icon file is called "AppIcon.icns".