Hi Puybaret,
I was thinking like you that I made an error modifying the file
[font=courier new]PluginFurnitureCatalog.properties[/font]
For that reason I have tested the process by unzipping an existing file .sh3f that was opened correctly by the FurnitureLibraryEditor and then zipped the folder just created without making any modification.
In this case there was no modification at the file [font=courier new]PluginFurnitureCatalog.properties[/font] and so it should be correct. Yet I cannot open it as it is corrupted.

Do you have any idea why I hit this strange behavior?
Any help is very much appreciated.
Thanks,
Giuseppe