I would have liked to just add a comment to Ticket #1000194, as I get just the same exception. However, as I didn't work out how to add a comment, I'll just file this as a new ticket.

I get this when double-clicking a .scala file in the project explorer:

Scala Eclipse plugin version number: 1.0.0.201012280047

eclipse.buildId=M20100909-0800
java.version=1.6.0_22
java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=linux, ARCH=x86, WS=gtk, NL=de_DE
Framework arguments: -product org.eclipse.epp.package.jee.product
Command-line arguments: -os linux -ws gtk -arch x86 -product org.eclipse.epp.package.jee.product


Error
Thu Dec 30 15:13:30 CET 2010
Problems occurred when invoking code from plug-in: "org.eclipse.jface".

java.lang.ExceptionInInitializerError
at scala.tools.eclipse.ScalaSourceViewerConfiguration$$anonfun$getHyperlinkDetectors$1.apply(ScalaSourceViewerConfiguration.scala:89)
at scala.tools.eclipse.ScalaSourceViewerConfiguration$$anonfun$getHyperlinkDetectors$1.apply(ScalaSourceViewerConfiguration.scala:88)
at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:206)
at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:206)
at scala.collection.IndexedSeqOptimized$class.foreach(IndexedSeqOptimized.scala:34)
at scala.collection.mutable.ArrayOps.foreach(ArrayOps.scala:35)
at scala.collection.TraversableLike$class.map(TraversableLike.scala:206)
at scala.collection.mutable.ArrayOps.map(ArrayOps.scala:35)
at scala.tools.eclipse.ScalaSourceViewerConfiguration.getHyperlinkDetectors(ScalaSourceViewerConfiguration.scala:88)
at org.eclipse.jface.text.source.SourceViewer.configure(SourceViewer.java:488)
at org.eclipse.jdt.internal.ui.javaeditor.JavaSourceViewer.configure(JavaSourceViewer.java:223)
at org.eclipse.ui.texteditor.AbstractTextEditor.createPartControl(AbstractTextEditor.java:3250)
at org.eclipse.ui.texteditor.StatusTextEditor.createPartControl(StatusTextEditor.java:53)
at org.eclipse.ui.texteditor.AbstractDecoratedTextEditor.createPartControl(AbstractDecoratedTextEditor.java:432)
at org.eclipse.jdt.internal.ui.javaeditor.JavaEditor.createPartControl(JavaEditor.java:3104)
at org.eclipse.jdt.internal.ui.javaeditor.CompilationUnitEditor.createPartControl(CompilationUnitEditor.java:1475)
at org.eclipse.ui.internal.EditorReference.createPartHelper(EditorReference.java:670)
at org.eclipse.ui.internal.EditorReference.createPart(EditorReference.java:465)
at org.eclipse.ui.internal.WorkbenchPartReference.getPart(WorkbenchPartReference.java:595)
at org.eclipse.ui.internal.PartPane.setVisible(PartPane.java:313)
at org.eclipse.ui.internal.presentations.PresentablePart.setVisible(PresentablePart.java:180)
at org.eclipse.ui.internal.presentations.util.PresentablePartFolder.select(PresentablePartFolder.java:270)
at org.eclipse.ui.internal.presentations.util.LeftToRightTabOrder.select(LeftToRightTabOrder.java:65)
at org.eclipse.ui.internal.presentations.util.TabbedStackPresentation.selectPart(TabbedStackPresentation.java:473)
at org.eclipse.ui.internal.PartStack.refreshPresentationSelection(PartStack.java:1254)
at org.eclipse.ui.internal.PartStack.setSelection(PartStack.java:1207)
at org.eclipse.ui.internal.PartStack.showPart(PartStack.java:1606)
at org.eclipse.ui.internal.PartStack.add(PartStack.java:497)
at org.eclipse.ui.internal.EditorStack.add(EditorStack.java:103)
at org.eclipse.ui.internal.PartStack.add(PartStack.java:483)
at org.eclipse.ui.internal.EditorStack.add(EditorStack.java:112)
at org.eclipse.ui.internal.EditorSashContainer.addEditor(EditorSashContainer.java:63)
at org.eclipse.ui.internal.EditorAreaHelper.addToLayout(EditorAreaHelper.java:225)
at org.eclipse.ui.internal.EditorAreaHelper.addEditor(EditorAreaHelper.java:213)
at org.eclipse.ui.internal.EditorManager.createEditorTab(EditorManager.java:778)
at org.eclipse.ui.internal.EditorManager.openEditorFromDescriptor(EditorManager.java:677)
at org.eclipse.ui.internal.EditorManager.openEditor(EditorManager.java:638)
at org.eclipse.ui.internal.WorkbenchPage.busyOpenEditorBatched(WorkbenchPage.java:2860)
at org.eclipse.ui.internal.WorkbenchPage.busyOpenEditor(WorkbenchPage.java:2768)
at org.eclipse.ui.internal.WorkbenchPage.access$11(WorkbenchPage.java:2760)
at org.eclipse.ui.internal.WorkbenchPage$10.run(WorkbenchPage.java:2711)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:2707)
at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:2691)
at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:2682)
at org.eclipse.jdt.internal.ui.javaeditor.EditorUtility.openInEditor(EditorUtility.java:378)
at org.eclipse.jdt.internal.ui.javaeditor.EditorUtility.openInEditor(EditorUtility.java:178)
at org.eclipse.jdt.ui.actions.OpenAction.run(OpenAction.java:229)
at org.eclipse.jdt.ui.actions.OpenAction.run(OpenAction.java:208)
at org.eclipse.jdt.ui.actions.SelectionDispatchAction.dispatchRun(SelectionDispatchAction.java:274)
at org.eclipse.jdt.ui.actions.SelectionDispatchAction.run(SelectionDispatchAction.java:250)
at org.eclipse.jdt.internal.ui.packageview.PackageExplorerActionGroup.handleOpen(PackageExplorerActionGroup.java:373)
at org.eclipse.jdt.internal.ui.packageview.PackageExplorerPart$4.open(PackageExplorerPart.java:526)
at org.eclipse.ui.OpenAndLinkWithEditorHelper$InternalListener.open(OpenAndLinkWithEditorHelper.java:48)
at org.eclipse.jface.viewers.StructuredViewer$2.run(StructuredViewer.java:845)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:49)
at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:175)
at org.eclipse.jface.viewers.StructuredViewer.fireOpen(StructuredViewer.java:843)
at org.eclipse.jface.viewers.StructuredViewer.handleOpen(StructuredViewer.java:1131)
at org.eclipse.jface.viewers.StructuredViewer$6.handleOpen(StructuredViewer.java:1235)
at org.eclipse.jface.util.OpenStrategy.fireOpenEvent(OpenStrategy.java:264)
at org.eclipse.jface.util.OpenStrategy.access$2(OpenStrategy.java:258)
at org.eclipse.jface.util.OpenStrategy$1.handleEvent(OpenStrategy.java:298)
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: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:619)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:574)
at org.eclipse.equinox.launcher.Main.run(Main.java:1407)
Caused by: java.lang.NoSuchMethodException: org.eclipse.jdt.internal.ui.text.java.hover.BestMatchHover.addTextHover(org.eclipse.jface.text.ITextHover)
at java.lang.Class.getDeclaredMethod(Class.java:1937)
at scala.tools.eclipse.util.ReflectionUtils$$anonfun$getDeclaredMethod$1.apply(ReflectionUtils.scala:42)
at scala.tools.eclipse.util.ReflectionUtils$$anonfun$getDeclaredMethod$1.apply(ReflectionUtils.scala:41)
at scala.tools.eclipse.util.ReflectionUtils$$anon$1.run(ReflectionUtils.scala:57)
at java.security.AccessController.doPrivileged(Native Method)
at scala.tools.eclipse.util.ReflectionUtils$class.privileged(ReflectionUtils.scala:56)
at scala.tools.eclipse.ScalaSourceViewerConfigurationUtils$.privileged(ScalaSourceViewerConfiguration.scala:152)
at scala.tools.eclipse.util.ReflectionUtils$class.getDeclaredMethod(ReflectionUtils.scala:41)
at scala.tools.eclipse.ScalaSourceViewerConfigurationUtils$.getDeclaredMethod(ScalaSourceViewerConfiguration.scala:152)
at scala.tools.eclipse.ScalaSourceViewerConfigurationUtils$.<init>(ScalaSourceViewerConfiguration.scala:154)
at scala.tools.eclipse.ScalaSourceViewerConfigurationUtils$.<clinit>(ScalaSourceViewerConfiguration.scala)
... 88 more