Hi,
I have a problem with the reconstruction of the subdivision levels on this model:
It’s an old and uncompleted model I would like to work on again, but unfortunately I found just the .obj file so I don’t have any subdivision level, and when I click on “reconstruct subdiv” I get an error which says: “Reconstruction result: Mesh contains triangles, operation cancelled.”
Any idea on how to fix this problem?
Thanks 
Reconstruct Subdiv only works on all-quad meshes and will not go back a level if there are any triangles in the current level.
You best solution is to use retopo tools or perhaps an outside package like Topogun or Modo to rebuild a simple base mesh, and then use Project All to transfer the details from this hi res .obj to the new base mesh, suitably subdivided.
-K
Thank you for the answer!
I started recreating the topology in zbrush but I got a problem with the “mouth area”.
BEFORE:
I guess I have this problem just because of my experience (few months) but it looks pretty hard to rebuild the topology of this part… Do you have any suggestion about it? It would be a bit easier with the tools your told me or I’m just doing something wrong with the topology?
Thanks for your help 
It’s just a tough area to retopo. 
It wouldn’t be much easier in other tools either.
If it was my project, I would probably go simpler in my base mesh, recognizing that the projection might be a little imperfect. After projecting, I’d just clean up the newly project mesh with the zproject brush or other sculpting tools.
(Sort of like cleaning up a casting after it’s been made from a mold in the real world . . .)
-K
Well… you were right XD I just completed the topology! It has pretty hard in that part, since inside it was an empty space.
However, thanks for the help!