Plugins can't access local file system when they are run within the Java Web Start version of Sweet Home 3D, and I release Beta version only under Java Web Start because it's much easier for me and can be tested under all systems. Therefore, you can't run the Export to SH3F plugin with current Beta.
I know this is annoying but I didn't fix this security issue yet. As I succeeded to fix it for applets, it should be possible for Java Web Start version too.
As the furniture catalog internal structure didn't evolve from version 2.2, you can install version 2.2 for Windows with its installer, install the Export to SH3F plugin, export your furniture catalog, uninstall Sweet Home 3D 2.2 and reinstall version 2.3 Beta to use the Group/Ungroup feature.
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Emmanuel Puybaret, Sweet Home 3D creator
