R integration using Kettle

Hi Team,

When i am trying to use the R Script Executor with an R Script i am getting the following error.

Unable to open dialog for this step
java.lang.NoClassDefFoundError: Could not initialize class weka.core.RSession
at org.pentaho.r.b.a(SourceFile:560)
at org.pentaho.di.trans.steps.rscriptexecutor.b.a(SourceFile:266)
at a.a.a.a.a.a.a.a.a(SourceFile:881)
at a.a.a.a.a.a.a.a$6.handleEvent(SourceFile:811)
at org.eclipse.swt.widgets.EventTable.sendEvent(Unknown Source)
at org.eclipse.swt.widgets.Widget.sendEvent(Unknown Source)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Unknown Source)
at org.eclipse.swt.widgets.Display.readAndDispatch(Unknown Source)
at a.a.a.a.a.a.a.a.open(SourceFile:267)
at org.pentaho.di.ui.spoon.delegates.SpoonStepsDelegate.editStep(SpoonStepsDelegate.java:124)
at org.pentaho.di.ui.spoon.Spoon.editStep(Spoon.java:8720)
at org.pentaho.di.ui.spoon.trans.TransGraph.editStep(TransGraph.java:3027)
at org.pentaho.di.ui.spoon.trans.TransGraph.mouseDoubleClick(TransGraph.java:744)
at org.eclipse.swt.widgets.TypedListener.handleEvent(Unknown Source)
at org.eclipse.swt.widgets.EventTable.sendEvent(Unknown Source)
at org.eclipse.swt.widgets.Widget.sendEvent(Unknown Source)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Unknown Source)
at org.eclipse.swt.widgets.Display.readAndDispatch(Unknown Source)
at org.pentaho.di.ui.spoon.Spoon.readAndDispatch(Spoon.java:1310)
at org.pentaho.di.ui.spoon.Spoon.waitForDispose(Spoon.java:7931)
at org.pentaho.di.ui.spoon.Spoon.start(Spoon.java:9202)
at org.pentaho.di.ui.spoon.Spoon.main(Spoon.java:648)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.pentaho.commons.launcher.Launcher.main(Launcher.java:92)