前幾天把GEF版本從3.0.1升級到了3.1M6，發現以前運行正常的GEF程式現在總出現下面這個異常，例如在我移動一個節點時，或者建立一個新節點時。
!ENTRY org.eclipse.ui 4 0 2005-04-19 23:12:55.974
!MESSAGE tried to access method org.eclipse.ui.views.properties.PropertySheetEntry.refreshFromRoot()V from class org.eclipse.gef.ui.properties.UndoablePropertySheetEntry
!STACK 0
java.lang.IllegalAccessError: tried to access method org.eclipse.ui.views.properties.PropertySheetEntry.refreshFromRoot()V from class org.eclipse.gef.ui.properties.UndoablePropertySheetEntry
at org.eclipse.gef.ui.properties.UndoablePropertySheetEntry.access$0(UndoablePropertySheetEntry.java:1)
at org.eclipse.gef.ui.properties.UndoablePropertySheetEntry$1.commandStackChanged(UndoablePropertySheetEntry.java:103)
at org.eclipse.gef.commands.CommandStack.notifyListeners(CommandStack.java:253)
at org.eclipse.gef.commands.CommandStack.execute(CommandStack.java:141)
at org.eclipse.gef.tools.AbstractTool.executeCommand(AbstractTool.java:374)
at org.eclipse.gef.tools.AbstractTool.executeCurrentCommand(AbstractTool.java:386)
at org.eclipse.gef.tools.DragEditPartsTracker.performDrag(DragEditPartsTracker.java:450)
at org.eclipse.gef.tools.DragEditPartsTracker.handleButtonUp(DragEditPartsTracker.java:320)
at org.eclipse.gef.tools.AbstractTool.mouseUp(AbstractTool.java:1035)
at org.eclipse.gef.tools.SelectionTool.mouseUp(SelectionTool.java:545)
at org.eclipse.gef.EditDomain.mouseUp(EditDomain.java:259)
at org.eclipse.gef.ui.parts.DomainEventDispatcher.dispatchMouseReleased(DomainEventDispatcher.java:374)
at org.eclipse.draw2d.LightweightSystem$EventHandler.mouseUp(LightweightSystem.java:548)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:136)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:82)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:842)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:2908)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:2541)
at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:1612)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:1578)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:293)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:144)
at org.eclipse.ui.internal.ide.IDEApplication.run(IDEApplication.java:102)
at org.eclipse.core.internal.runtime.PlatformActivator$1.run(PlatformActivator.java:228)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:333)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:150)
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:268)
at org.eclipse.core.launcher.Main.basicRun(Main.java:260)
at org.eclipse.core.launcher.Main.run(Main.java:887)
at org.eclipse.core.launcher.Main.main(Main.java:871)
調試了很久也沒找到原因，最後在GEF新聞群組裡得到了答案，原來GEF3.1M6要求Eclipse的版本在3.1M6或以上，而我正在使用的是Eclipse 3.1M5a，換到3.1M6一試果然OK。
如果你遇到類似的奇怪異常，不妨也先檢查一下Eclipse和外掛程式的版本。
