I have the same issue on the Mac. The plugin is located at:
~/Library/Application Support/eTeks/Sweet Home 3D/plugins/VolumePlugin.jar

PluginManager.loadPlugins tries to load him and throws an exception when he calls readPlugin.
[font=courier new]readPlugin(ResourceBundle.getBundle(applicationPluginFamily, Locale.getDefault(), classLoader),
pluginLocation,
"jar:" + pluginUrl.toString() + "!/" + URLEncoder.encode(zipEntryName, "UTF-8").replace("+", "%20"),
classLoader);[/font]

He appears to searching for 'ApplicationPlugin' in the bundle. The jar does contain the ApplicationPlugin.properties file. For sure, there's nothing much wrong here, however I don't know how to fix it!