'LIB ERROR: object lost from scene' error when opening file When I tried to load the attached blend-file a few minutes after saving it, I got the message 'LIB ERROR: object lost from scene', and I realized that a tunnel I had made around the road was lost!

The mesh object that was lost was a cylinder named 'TUNNEL'. Like the other mesh objects ('ROAD', 'SIDEWALK LEFT' and 'SIDEWALK RIGHT') it had an array followed by a curve modifier, that made it follow the 'ALIGNMENT' path.

I checked the last Quit.blend, it had the same problem. Too, with the last autosave.

I am, once again, completely baffled. Can anyone make heads or tails out of it?
I can't say why this has happened, but your tunnel is still in the file.

Make a duplicate of the 'ROAD' object, go to the duplicate 'ROAD's Data panel, and then select the data that has a '0' next to it:



This should assign the mesh datablock back to an object and your duplicate road should now be your tunnel. The '0' next to the mesh datablock meant that the mesh wasn't being used (as it wasn't assigned to any object). 

From what I've read about the error you got it refers to objects that were linked from other files, and then the object in the original file has been renamed, breaking the link, meaning blender is unable to find and load the object. 

However, there are some reports of this happening without any renaming, which if you are able to reproduce it, should be reported as a bug report here (or added to that bug report I linked to).