error in log

Not sure why but get this...

org.eclipse.swt.SWTException: Failed to execute runnable (java.lang.ClassCastException: java.lang.String cannot be cast to org.eclipse.zest.layouts.dataStructures.InternalNode)
at org.eclipse.swt.SWT.error(SWT.java:4282)
at org.eclipse.swt.SWT.error(SWT.java:4197)
at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:138)
at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:3938)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3615)
at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2701)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2665)
at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2499)
at org.eclipse.ui.internal.Workbench$7.run(Workbench.java:679)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:668)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:123)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:344)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:622)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:577)
at org.eclipse.equinox.launcher.Main.run(Main.java:1410)
Caused by: java.lang.ClassCastException: java.lang.String cannot be cast to org.eclipse.zest.layouts.dataStructures.InternalNode
at org.fusesource.ide.graph.DirectedDiagramViewLayoutAlgorithm.adjustHorizontalSpaces(DirectedDiagramViewLayoutAlgorithm.java:95)
at org.fusesource.ide.graph.DirectedDiagramViewLayoutAlgorithm.applyLayoutInternal(DirectedDiagramViewLayoutAlgorithm.java:65)
at org.eclipse.zest.layouts.algorithms.AbstractLayoutAlgorithm.applyLayout(AbstractLayoutAlgorithm.java:481)
at org.eclipse.zest.core.widgets.Graph.applyLayoutInternal(Graph.java:1131)
at org.eclipse.zest.core.widgets.Graph.access$6(Graph.java:1090)
at org.eclipse.zest.core.widgets.Graph$6.run(Graph.java:421)
at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:35)
at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:135)
... 22 more