Access restriction error in eclipse

[Steffan]

Hi, I'm trying to include J3D classes (Java3d) into my eclipse project. But when I write for example:

import com.sun.j3d.utils.universe.SimpleUniverse;

Then I get an error saying "Access restriction: The type SimpleUniverse is not accessible due to restriction on required library C:\Programfiler\Java\jre6\lib\ext\j3ddutils.jar"

The jar's is locked, because all files in "program files" always is locked. Could this be the problem? If so; How to get eclipse to change the classpath to another file with the J3D jar's?

Also when I compile and run I get:

Exception in thread "main" java.lang.Error: Unresolved compilation problem at IEC3D.main(IEC3D.java:25)

Here is my whole code:

import com.sun.j3d.utils.universe.SimpleUniverse;

import com.sun.j3d.utils.geometry.ColorCube;

import javax.media.j3d.BranchGroup;

public class IEC3D {

public IEC3D()

{

   SimpleUniverse universe = new SimpleUniverse();

   BranchGroup group = new BranchGroup();

   group.addChild(new ColorCube(0.3));

   universe.getViewingPlatform().setNominalViewingTransform();

   universe.addBranchGraph(group);

}

public static void main( String[] args ) {

   new IEC3D();

}

} // end of class Hello3d

Edit:
I found the problem, and suddenly it was fixed. I doesn't exactly know how it got fixed, but it was something with the path access... I think I included a path to some other jar's where I got access.