Landscape material error with shading model: "From Material Expression".

Hello, I have a main landscape material, each layer as a material function connected to layer blend node… and everything is fine until i plugged in each material a “shading model” node. I have 5 materials “default lit” and 2 materials (snow & ice) as “Subsurface”.

But when , in the main landscape material , I switch between default lit to “From Material Expression”. I get an error: “Node LandscapeLayerBlend: Arithmetic between types ShadingModel and float are undefined.” What does it mean? How can I do?