isc.isA.DrawItem is not a function!what is mean

i use FormBuilderSample demo in gwt2.5,but when it running,
the errors happened:

Unable to load module entry point class com.rd.ilp.client.FormBuilderSample (see associated exception for details)
com.google.gwt.core.client.JavaScriptException: (TypeError) @com.smartgwt.client.widgets.BaseWidget::draw()([]): isc.isA.DrawItem is not a function
at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:249)
at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136)
at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:571)
at com.google.gwt.dev.shell.ModuleSpace.invokeNativeVoid(ModuleSpace.java:299)
at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeVoid(JavaScriptHost.java:107)
at com.smartgwt.client.widgets.BaseWidget.draw(BaseWidget.java)
at com.rd.ilp.client.FormBuilderSample.onModuleLoad(FormBuilderSample.java:443)
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.ModuleSpace.onLoad(ModuleSpace.java:406)
at com.google.gwt.dev.shell.OophmSessionHandler.loadModule(OophmSessionHandler.java:200)
at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:526)
at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:364)
at java.lang.Thread.run(Thread.java:662)

what can i do?