the .obj file in jmonkeyengine.com tutorial

Hi everyone :
I am new to graphics , I have been trying load a object created in 3Dmax 8.0to Java3D,. I exported it from 3Dmax as a .obj file ,but I couldn't get the correct .mtl file which will
be needed . Does anyone know how to get a correct .mtl file. ?? The .mtl file I got is as below:

# Max2Mtl Version 4.0 Mar 10th, 2001
#
# EOF

which doesn't work.

I tried to use the Loader in jme.jar to load the .obj exported from 3D max 8.0, it doesn't work . But it works for the .obj in the example
from the jmonkeyengine.com tutorials .

which is shown as below :

* Copyright (c) 2003-2006 jMonkeyEngine
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* * Neither the name of 'jMonkeyEngine' nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

package jmetest.TutorialGuide;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.net.URL;
import java.util.logging.Level;
import java.util.logging.Logger;

import com.jme.app.AbstractGame;
import com.jme.app.SimpleGame;
import com.jme.bounding.BoundingSphere;
import com.jme.scene.Node;
import com.jme.util.export.binary.BinaryImporter;
import com.jmex.model.converters.FormatConverter;
import com.jmex.model.converters.ObjToJme;

/**
* Started Date: Jul 22, 2004

*
* Demonstrates loading formats.
*
* @author Jack Lindamood
*/
public class HelloModelLoading extends SimpleGame {
private static final Logger logger = Logger
.getLogger(HelloModelLoading.class.getName());

public static void main(String[] args) {
HelloModelLoading app = new HelloModelLoading();
app.setDialogBehaviour(AbstractGame.ALWAYS_SHOW_PROPS_DIALOG);
// Turn the logger off so we can see the XML later on
app.start();
}

protected void simpleInitGame() {
// Point to a URL of my model
URL model=HelloModelLoading.class.getClassLoader().getResource("jmetest/data/model/maggie.obj");

// Create something to convert .obj format to .jme
FormatConverter converter=new ObjToJme();
// Point the converter to where it will find the .mtl file from
converter.setProperty("mtllib",model);

// This byte array will hold my .jme file
ByteArrayOutputStream BO=new ByteArrayOutputStream();
try {
// Use the format converter to convert .obj to .jme
converter.convert(model.openStream(), BO);
Node maggie=(Node)BinaryImporter.getInstance().load(new ByteArrayInputStream(BO.toByteArray()));
// shrink this baby down some
maggie.setLocalScale(.1f);
maggie.setModelBound(new BoundingSphere());
maggie.updateModelBound();
// Put her on the scene graph
rootNode.attachChild(maggie);
} catch (IOException e) { // Just in case anything happens
logger.logp(Level.SEVERE, this.getClass().toString(),
"simpleInitGame()", "Exception", e);
System.exit(0);
}
}
}

I changed "the jmetest/data/model/maggie.obj" to the .obj file exported from 3Dmax , it generates an error everytime I tried to run it.

Exception in game loop
java.lang.ClassCastException: com.jme.scene.TriMesh cannot be cast to com.jme.scene.Node
at jmetest.TutorialGuide.HelloModelLoading.simpleInitGame(HelloModelLoading.java:82)
at com.jme.app.BaseSimpleGame.initGame(BaseSimpleGame.java:503)
at com.jme.app.BaseGame.start(BaseGame.java:69)
at jmetest.TutorialGuide.HelloModelLoading.main(HelloModelLoading.java:65)
2007-3-16 11:24:29 com.jme.app.BaseSimpleGame cleanup

can anyone help? ???Many thanks