2 landscapes, cannot apply materials to 2nd one

Hi, I am really new… and I’m having fun learning but I have found a problem I haven’t been able to find a solution. I have a large landscape and added a lake. My son said put in an underwater cave etc. I did. So I sculpted the cave etc on the large landscape. 64x64 and looked at different ways I could make the roof. Finally I decided to try adding a second landscape over the top of the carved out area thus providing a roof. This is a smaller landscape, 15x15. It all fit in nicely and I could sculpt the smaller landscape. However, when I applied the material inst I used to paint the large landscape and tried to paint on the smaller one and I get the message: This layer has no layer info assigned yet. So, I tried to assign the layers in the material as I did when I set it up for the large landscape and save it… I get the message that the name already exists. I have tried duplicating the material inst, renaming it, putting it in a different folder… and still I get the same message and I cannot assign the layer info. How do you apply material layers, or textures to more than one landscape? I’m totally lost. Thanks in advance for any help at all.