bdfd, thanks for your tests. Apparently the file bug in Windows 10 Creator update wasn't fixed in beta 6 yet, but I have other ideas, better than obliging users to add a SweetHome3D.l4j.ini file.
Here's the version 5.5 Beta 7 (Java Web Start version and Windows installer) that might fix that bug. It would be nice if you and/or harhouse could report if showing file dialog boxes works better in this version.

This Beta version brings also auto translation of furniture names found in demos, and the first translations of the new features in Italian, Portuguese, Dutch, Czech, and Polish made by the nice Sweet Home 3D contributors. Finally, it fixes again an other small issue about furniture rotated around an horizontal axis (a really tough subject as I feared!!!).