DualDepthPeeling demo fails to link shaders

Hi,
I'm running the peeling demo and see the following message in console.
Do you have suggestions on how to know a little more about the link failure root cause?
Cheers,
Martin

createAndCompileShader: Pre GL Error: 0x501
Shader status invalid: (no info log)
Exception in thread "main-AWTAnimator-1" java.lang.RuntimeException: javax.media.opengl.GLException: Couldn't link program: ShaderProgram[id=1, linked=false, inUse=false, program: 10092713,
   ShaderCode[id=1, type=VERTEX_SHADER, valid=false, shader:  10092712, source]
   ShaderCode[id=2, type=FRAGMENT_SHADER, valid=false, shader:  0, source]]
Basenames:dual_peeling_init
        at jogamp.common.awt.AWTEDTExecutor.invoke(AWTEDTExecutor.java:58)
        at jogamp.opengl.awt.AWTThreadingPlugin.invokeOnOpenGLThread(AWTThreadingPlugin.java:103)
        at jogamp.opengl.ThreadingImpl.invokeOnOpenGLThread(ThreadingImpl.java:206)
        at javax.media.opengl.Threading.invokeOnOpenGLThread(Threading.java:172)
        at javax.media.opengl.Threading.invoke(Threading.java:191)
        at javax.media.opengl.awt.GLCanvas.display(GLCanvas.java:428)
        at com.jogamp.opengl.util.AWTAnimatorImpl.display(AWTAnimatorImpl.java:74)
        at com.jogamp.opengl.util.AnimatorBase.display(AnimatorBase.java:142)
        at com.jogamp.opengl.util.Animator$MainLoop.run(Animator.java:176)
        at java.lang.Thread.run(Thread.java:679)
Caused by: javax.media.opengl.GLException: Couldn't link program: ShaderProgram[id=1, linked=false, inUse=false, program: 10092713,
   ShaderCode[id=1, type=VERTEX_SHADER, valid=false, shader:  10092712, source]
   ShaderCode[id=2, type=FRAGMENT_SHADER, valid=false, shader:  0, source]]
Basenames:dual_peeling_init
        at demos.dualDepthPeeling.DualDepthPeeling.build(DualDepthPeeling.java:440)
        at demos.dualDepthPeeling.DualDepthPeeling.BuildShaders(DualDepthPeeling.java:466)
        at demos.dualDepthPeeling.DualDepthPeeling.init(DualDepthPeeling.java:1022)
        at jogamp.opengl.GLDrawableHelper.init(GLDrawableHelper.java:201)
        at jogamp.opengl.GLDrawableHelper.init(GLDrawableHelper.java:222)
        at javax.media.opengl.awt.GLCanvas$6.run(GLCanvas.java:926)
        at jogamp.opengl.GLDrawableHelper.invokeGLImpl(GLDrawableHelper.java:521)
        at jogamp.opengl.GLDrawableHelper.invokeGL(GLDrawableHelper.java:462)
        at javax.media.opengl.awt.GLCanvas$9.run(GLCanvas.java:964)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:216)
        at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:670)
        at java.awt.EventQueue.access$400(EventQueue.java:96)
        at java.awt.EventQueue$2.run(EventQueue.java:631)
        at java.awt.EventQueue$2.run(EventQueue.java:629)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:105)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:640)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:275)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:200)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:185)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:177)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:138)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at demos.dualDepthPeeling.DualDepthPeeling.DrawModel(DualDepthPeeling.java:409)
        at demos.dualDepthPeeling.DualDepthPeeling.RenderDualPeeling(DualDepthPeeling.java:581)
        at demos.dualDepthPeeling.DualDepthPeeling.display(DualDepthPeeling.java:974)
        at jogamp.opengl.GLDrawableHelper.displayImpl(GLDrawableHelper.java:243)
        at jogamp.opengl.GLDrawableHelper.display(GLDrawableHelper.java:230)
        at javax.media.opengl.awt.GLCanvas$7.run(GLCanvas.java:943)
        at jogamp.opengl.GLDrawableHelper.invokeGLImpl(GLDrawableHelper.java:523)
        at jogamp.opengl.GLDrawableHelper.invokeGL(GLDrawableHelper.java:462)
        at javax.media.opengl.awt.GLCanvas$9.run(GLCanvas.java:964)
        at javax.media.opengl.Threading.invoke(Threading.java:193)
        at javax.media.opengl.awt.GLCanvas.display(GLCanvas.java:428)
        at javax.media.opengl.awt.GLCanvas.paint(GLCanvas.java:480)
        at sun.awt.RepaintArea.paintComponent(RepaintArea.java:264)
        at sun.awt.X11.XRepaintArea.paintComponent(XRepaintArea.java:73)
        at sun.awt.RepaintArea.paint(RepaintArea.java:240)
        at sun.awt.X11.XComponentPeer.handleEvent(XComponentPeer.java:657)
        at java.awt.Component.dispatchEventImpl(Component.java:4826)
        at java.awt.Component.dispatchEvent(Component.java:4576)
        at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:672)
        at java.awt.EventQueue.access$400(EventQueue.java:96)
        at java.awt.EventQueue$2.run(EventQueue.java:631)
        at java.awt.EventQueue$2.run(EventQueue.java:629)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:105)
        at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:116)
        at java.awt.EventQueue$3.run(EventQueue.java:645)
        at java.awt.EventQueue$3.run(EventQueue.java:643)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:105)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:642)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:275)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:200)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:185)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:177)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:138)