Max texture number in landscape material

I have a problem when apliyng a material to the landscape.
I created the material with
+6 albedo color maps
+6 normal maps

When finished the “Compiling shaders” popup message the material is not applied.

Only works if I use:
+4 color maps
+4 Normal maps

The texture samplers are less than 16 in both cases.

¿why?