"Asset cannot be saved as it has only been partially loaded"

Every time I import a .fbx from Autocad, I can’t save it. When I import it, I’m told that “No smoothing group was found in this scene, blablabla…” But normally I don’t think that should cause a problem. Right? Any solutions would be extremely welcome, as I’ve been swearing at my pc for the last day.
Here’s a link to my fbx: Google Drive: Sign-in