Error opening editors NoClassDefFound org/jboss/tools/jst/jsp/jspeditor/JSPMultiPageEditor

eclipse.buildId=M20100909-0800
java.version=1.6.0_18
java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=linux, ARCH=x86, WS=gtk, NL=en_US
Framework arguments: -product org.eclipse.epp.package.jee.product -product org.eclipse.epp.package.jee.product -product org.eclipse.epp.package.jee.product
Command-line arguments: -os linux -ws gtk -arch x86 -product org.eclipse.epp.package.jee.product -product org.eclipse.epp.package.jee.product -data /working/workspace/default -product org.eclipse.epp.package.jee.product

Error
Tue Nov 23 04:41:30 EST 2010
Problems occurred when invoking code from plug-in: "org.eclipse.ui.workbench".

java.lang.NoClassDefFoundError: org/jboss/tools/jst/jsp/jspeditor/JSPMultiPageEditor
at org.jboss.tools.jsf.ui.editor.check.ProjectNaturesPartListener.checkNaturesFromPart(ProjectNaturesPartListener.java:72)
at org.jboss.tools.jsf.ui.editor.check.ProjectNaturesPartListener.partOpened(ProjectNaturesPartListener.java:62)
at org.eclipse.ui.internal.PartListenerList$5.run(PartListenerList.java:132)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.runtime.Platform.run(Platform.java:888)
at org.eclipse.ui.internal.PartListenerList.fireEvent(PartListenerList.java:57)
at org.eclipse.ui.internal.PartListenerList.firePartOpened(PartListenerList.java:130)
at org.eclipse.ui.internal.PartService.firePartOpened(PartService.java:276)
at org.eclipse.ui.internal.WWinPartService$WWinListener.partOpened(WWinPartService.java:54)
at org.eclipse.ui.internal.PartListenerList2$5.run(PartListenerList2.java:130)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.runtime.Platform.run(Platform.java:888)
at org.eclipse.ui.internal.PartListenerList2.fireEvent(PartListenerList2.java:55)
at org.eclipse.ui.internal.PartListenerList2.firePartOpened(PartListenerList2.java:128)
at org.eclipse.ui.internal.PartService.firePartOpened(PartService.java:280)
at org.eclipse.ui.internal.WorkbenchPagePartList.firePartOpened(WorkbenchPagePartList.java:35)
at org.eclipse.ui.internal.PartList.partOpened(PartList.java:241)
at org.eclipse.ui.internal.PartList.access$0(PartList.java:210)
at org.eclipse.ui.internal.PartList$1.propertyChanged(PartList.java:40)
at org.eclipse.ui.internal.WorkbenchPartReference.fireInternalPropertyChange(WorkbenchPartReference.java:375)
at org.eclipse.ui.internal.WorkbenchPartReference.getPart(WorkbenchPartReference.java:610)
at org.eclipse.ui.internal.Perspective.showView(Perspective.java:2245)
at org.eclipse.ui.internal.WorkbenchPage.busyShowView(WorkbenchPage.java:1071)
at org.eclipse.ui.internal.WorkbenchPage$20.run(WorkbenchPage.java:3822)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.ui.internal.WorkbenchPage.showView(WorkbenchPage.java:3819)
at org.eclipse.ui.internal.WorkbenchPage.showView(WorkbenchPage.java:3795)
at org.eclipse.ui.handlers.ShowViewHandler.openView(ShowViewHandler.java:162)
at org.eclipse.ui.handlers.ShowViewHandler.openOther(ShowViewHandler.java:106)
at org.eclipse.ui.handlers.ShowViewHandler.execute(ShowViewHandler.java:74)
at org.eclipse.ui.internal.handlers.HandlerProxy.execute(HandlerProxy.java:293)
at org.eclipse.core.commands.Command.executeWithChecks(Command.java:476)
at org.eclipse.core.commands.ParameterizedCommand.executeWithChecks(ParameterizedCommand.java:508)
at org.eclipse.ui.internal.handlers.HandlerService.executeCommand(HandlerService.java:169)
at org.eclipse.ui.internal.handlers.SlaveHandlerService.executeCommand(SlaveHandlerService.java:241)
at org.eclipse.ui.internal.ShowViewMenu$3.run(ShowViewMenu.java:144)
at org.eclipse.jface.action.Action.runWithEvent(Action.java:498)
at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:584)
at org.eclipse.jface.action.ActionContributionItem.access$2(ActionContributionItem.java:501)
at org.eclipse.jface.action.ActionContributionItem$5.handleEvent(ActionContributionItem.java:411)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1258)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3540)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3161)
at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2640)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2604)
at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2438)
at org.eclipse.ui.internal.Workbench$7.run(Workbench.java:671)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:664)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:115)
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:369)
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:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:619)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:574)
at org.eclipse.equinox.launcher.Main.run(Main.java:1407)