RawHeightMap Error

I'm trying to load the .raw height map file from TestIsland.java, but I always get this strange error:

com.jme.system.JmeException: Must supply valid resource and size (> 0)

The code I'm using is exactly the same as TestIsland.java:

RawHeightMap heightMap = new RawHeightMap(Main.class
                129, RawHeightMap.FORMAT_16BITLE, false);

        Vector3f terrainScale = new Vector3f(5, 0.003f, 6);
        TerrainPage page = new TerrainPage("Terrain", 33, heightMap.getSize(),
                terrainScale, heightMap.getHeightMap());


I don't know why that's happening! Help please?

I asume the resource is not in the classpath.