Why are you posting in the Unity forum? Does your workflow have anything with Unity at all?
Sprite Lamp may not have been updated to support the latest version of Spine jsons.
Though if you are using Unity, you shouldn't need to use Sprite Lamp to preview. You can preview them in Unity just fine with better control over the material and lights. The spine-unity unitypackage comes bundled with sprite shaders that support normal maps.
Also see the Sprite Shaders sample scene in the unitypackage. The normal maps there were created using Sprite Lamp.
I can't say Sprite Lamp is the fastest/easiest way to make normal maps for your sprites but it does give you some degree of control, especially the freedom to disobey how surfaces would actually work.
But it gets rather time consuming if you have a lot of individual images, since it essentially requires you to paint 5 lighting conditions per part. But again, that's great if you want that level of control, or don't have a lot of image parts per character.
We haven't tried Sprite DLight yet.
CodeAndWeb's SpriteIlluminator seems like the click-and-go solution if you have a huge number of simple assets that just need basic lighting and a tiny bit of adjustment. But if your style involves many seamlessly overlapping parts, it may involve some amount of manual adjustment in the context of the parts, which it currently doesn't support.
Your last option, as far as I know, is really to paint normals manually with Photoshop or any painting program.
You would just paint the image parts with the color corresponding to where the surface is theoretically facing: http://inpursuitofoptimal.blogspot.com/2015/01/normal-map-palette.html
You can still preview them using Unity by updating the assets.
You could also use this manual-painting method to correct any imperfect results you get from the programs mentioned.
So unfortunately, none of these solutions are perfect right now.
I'm summoning other users to chime in though. I know we have a few here: Sprite Shaders for Unity
