The error message means that no triangles were found in the project file for the mesh, or it could be that somehow no bones are bounds to the mesh. You could try editing the mesh in 4.1, just move a vertex in edit mesh mode. That should ensure the mesh has a valid triangulation. Then save and open with 4.2.
How does it look in edit mesh mode in 4.2?
While I would prefer your mesh didn't get messed up, if it is just the one mesh, it may be easiest to recreate it in 4.2.
