How can I paint a landscape with four textures?

I have a problem where I can paint with only three textures, Dirt, GrassDry, GrassLush, and Rock. But the rock causes the landscape to turn into the default checker board texture. The thing about it is I can only paint around the edges with the white colored rock texture, but it messes up in the middle. I’ve already tried building the shaders; but that didn’t work.