Ok, Your screenshot says it all ^^ Basically You can’t leave the UVs input empty. Most people just plug in the LandscapeLayerCoords node and set the mapping scale (the size of landscape in Your case) in details panel, but for more control I prefere to use Z projection, where I can set te scale via material instance.
EDIT: When using Z projection on landscape probably You will have to offset the texture to the landscape pivot point. Plug an Add node with a 2Vector set to X and Y location of the landscape pivot between Divide and TextureSample.
EDIT 2: I checked it on a 63x63 quads landscape and apparently You also have to divide the location by 8 for some reason.
