Hi Marius, I compiled my code, but all the buttons are invisible and uncaught exception came up: [ERROR] Uncaught exception escaped java.lang.RuntimeException: Failed to invoke native method: @org.xwiki.gwt.dom.client.Event::isCancelled() with 0 arguments. at com.google.gwt.dev.shell.moz.LowLevelMoz.invoke(LowLevelMoz.java:134) at com.google.gwt.dev.shell.moz.ModuleSpaceMoz.doInvoke(ModuleSpaceMoz.java:99) at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:453) at com.google.gwt.dev.shell.ModuleSpace.invokeNativeBoolean(ModuleSpace.java:146) at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeBoolean(JavaScriptHost.java:35) at org.xwiki.gwt.dom.client.Event$.isCancelled$(Event.java) at org.xwiki.gwt.user.client.ui.rta.internal.BehaviorAdjuster.onBrowserEvent(BehaviorAdjuster.java:123) at org.xwiki.gwt.user.client.ui.rta.RichTextArea.onBrowserEvent(RichTextArea.java:154) at com.google.gwt.user.client.DOM.dispatchEventImpl(DOM.java:1320) at com.google.gwt.user.client.DOM.dispatchEventAndCatch(DOM.java:1299) at com.google.gwt.user.client.DOM.dispatchEvent(DOM.java:1262) 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 com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103) at com.google.gwt.dev.shell.moz.MethodDispatch.invoke(MethodDispatch.java:80) at org.eclipse.swt.internal.gtk.OS._g_main_context_iteration(Native Method) at org.eclipse.swt.internal.gtk.OS.g_main_context_iteration(OS.java:1428) at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:2840) at com.google.gwt.dev.SwtHostedModeBase.processEvents(SwtHostedModeBase.java:235) at com.google.gwt.dev.HostedModeBase.pumpEventLoop(HostedModeBase.java:558) at com.google.gwt.dev.HostedModeBase.run(HostedModeBase.java:405) at com.google.gwt.dev.HostedMode.main(HostedMode.java:232) Here is the visual: https://docs.google.com/Doc?docid=0AUvGk3CNC6BPZGhwZGQ1M3dfNDNnNDQ5emZmNw&a… Could you please help me take a look at it. Thank you, Marius! Jue Wang