3ds Max :: Split UV Tiles

Sometimes when UV unwrapping, the map, for some reason ends up as individual tiles, even though the mesh is a single object. How can I fix that? Every single polygon has thick, green lines - like seams. When generating normal maps, it simply comes back as 'squares' of nothing, but laid out accordingly to the UV layout, so it's useless and holds no detail what-so-ever.

There are no inverted faces or overlapping faces, so that is not it. I can't weld every single vertex - there are thousands of them, of course, so it's rather baffling. The vertices, though, are connected, so that too is not the problem.