Is it possible to use a model with more than one group and have a normal map shader on it?

I tried to put the 2 textures (diffuse map and normal map) to one group of my model, but it isnt possible so long I have more than one group in the model.

If I look into the skin editor allways one of the maps have "no group selected". If I delete the other groups it works.

Kind regards

Taratoga