Problems occurred when invoking code from plug-in: "org.eclipse.ui.workbench"

J'ai cette erreur à chaque fois que je veux ouvrir un fichier
Code:
Problems occurred when invoking code from plug-in: "org.eclipse.ui.workbench"
voila la stacktrace :
Code:
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java.lang.NoClassDefFoundError: org/eclipse/jst/jsf/core/internal/provisional/jsfappconfig/JSFAppConfigUtils
	at org.eclipse.jst.jsf.designtime.internal.jsp.StartupHandler$JSPEditorListener.isValidJSPEditor(StartupHandler.java:171)
	at org.eclipse.jst.jsf.designtime.internal.jsp.StartupHandler$JSPEditorListener.isValidJSPEditor(StartupHandler.java:180)
	at org.eclipse.jst.jsf.designtime.internal.jsp.StartupHandler$JSPEditorListener.partClosed(StartupHandler.java:112)
	at org.eclipse.ui.internal.PartListenerList2$3.run(PartListenerList2.java:98)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:37)
	at org.eclipse.core.runtime.Platform.run(Platform.java:843)
	at org.eclipse.ui.internal.PartListenerList2.fireEvent(PartListenerList2.java:53)
	at org.eclipse.ui.internal.PartListenerList2.firePartClosed(PartListenerList2.java:96)
	at org.eclipse.ui.internal.PartService.firePartClosed(PartService.java:103)
	at org.eclipse.ui.internal.WWinPartService$1.partClosed(WWinPartService.java:44)
	at org.eclipse.ui.internal.PartListenerList2$3.run(PartListenerList2.java:98)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:37)
	at org.eclipse.core.runtime.Platform.run(Platform.java:843)
	at org.eclipse.ui.internal.PartListenerList2.fireEvent(PartListenerList2.java:53)
	at org.eclipse.ui.internal.PartListenerList2.firePartClosed(PartListenerList2.java:96)
	at org.eclipse.ui.internal.PartService.firePartClosed(PartService.java:103)
	at org.eclipse.ui.internal.WorkbenchPagePartList.firePartClosed(WorkbenchPagePartList.java:38)
	at org.eclipse.ui.internal.PartList.partClosed(PartList.java:255)
	at org.eclipse.ui.internal.PartList.removePart(PartList.java:176)
	at org.eclipse.ui.internal.WorkbenchPage.disposePart(WorkbenchPage.java:1540)
	at org.eclipse.ui.internal.WorkbenchPage.handleDeferredEvents(WorkbenchPage.java:1311)
	at org.eclipse.ui.internal.WorkbenchPage.deferUpdates(WorkbenchPage.java:1295)
	at org.eclipse.ui.internal.WorkbenchPage.closeEditors(WorkbenchPage.java:1269)
	at org.eclipse.ui.internal.EditorStack.close(EditorStack.java:218)
	at org.eclipse.ui.internal.PartStack$1.close(PartStack.java:106)
	at org.eclipse.ui.internal.presentations.SystemMenuCloseAll.run(SystemMenuCloseAll.java:32)
	at org.eclipse.jface.action.Action.runWithEvent(Action.java:499)
	at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:539)
	at org.eclipse.jface.action.ActionContributionItem.access$2(ActionContributionItem.java:488)
	at org.eclipse.jface.action.ActionContributionItem$5.handleEvent(ActionContributionItem.java:400)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:66)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:928)
	at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3348)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:2968)
	at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:1914)
	at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:1878)
	at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:419)
	at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
	at org.eclipse.ui.internal.ide.IDEApplication.run(IDEApplication.java:95)
	at org.eclipse.core.internal.runtime.PlatformActivator$1.run(PlatformActivator.java:78)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:92)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:68)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:400)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:177)
	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.eclipse.core.launcher.Main.invokeFramework(Main.java:336)
	at org.eclipse.core.launcher.Main.basicRun(Main.java:280)
	at org.eclipse.core.launcher.Main.run(Main.java:977)
	at org.eclipse.core.launcher.Main.main(Main.java:952)
Savez vous d'où ça vient ?

Merci