The file you shared contains only zeros i.e. no actual data. This error happens rarely and nobody found a way to reproduce it, so I can't fix it. Nevertheless, I had an idea to circumvent this issue in version 6.0 and wonder if you use this version or a more recent version. Is it the case? Any other hint which could help me understand how it happened?

Anyway maybe you can use this tip to recover recently opened files:
Look in the sub folders of [font=courier new]C:\Users\user\AppData\Roaming\eTeks\Sweet Home 3D\work[/font] (where user is your login name) if you can find some files starting by [font=courier new]open[/font] and suffixed by [font=courier new].sweethome3d[/font]. If there's any, it will contain the a copy of the document you recently opened. Copy the most recent file(s), change its extension to [font=courier new].sh3d[/font] and try to open it with Sweet Home 3D.