Sprite with normal map - why black?

Unity Engine
1

I want to expand 2D Toolkit sprite to show normal map. So I took unity build in transparent diffuse bump shader, and passed diffuse and normal sprite maps to it. But results is totally black image! (but transparent as it should be)
Any idea why?

2

The sprite may not have normals or tangents (both are required for normal mapping to work properly.

3

Thanks for the tip! I have where to start now, will see what google tells