Procedural mesh renders black

Hi,

I have a script which procedurally generates a terrain mesh at run-time. I've used shader forge to create a shader that blends between two different defuse and normal textures based on the world-space height of the terrain.

When applying this shader to a primitive like a sphere, it works fine. However, when applying it to the run-time generated mesh, I get a totally black mesh.

I suspect that this is todo with the lighting, because if I set the ambient lighting to a high value, or of i set the shader to an unlit shader, I can see the texture is applied to the mesh as expected, however none of the lights in the scene are picked up.

I expect that I'm doing something dumb, but after an hour of googling and tweaking random settings in the shader forge editor, I cannot get the mesh to pick up the lights.

What info do you need to help me debug this?

Thanks,

Lars