Zkoss - Erro no button

Amigos acabou de acontecer um erro estranho, quando adiciono a linha


<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

no código :

<zk>


<window title="SIG - APOENA" width="770px" border="normal"  
use="br.com.apoena.scripts.Usuario" id="usuarioClasse">

 <separator/>

<groupbox>
	<listbox id="box" multiple="true"  rows="5" onSelect="usuarioClasse.move()">
	  <listhead>
	   <listheader label="Cod. Usuario" />
	   <listheader label="Empresa" />   
	   <listheader label="Perfil" />
	  </listhead>
	
	  <listitem forEach="${usuarioClasse.todosUsuarios}" value="${each}">
		   <listcell label="${each.usuario}" />
		   <listcell label="${each.empresa}" />
		   <listcell label="${each.perfil}" />	   
	  </listitem>
	
	 </listbox>
	
	   
	      <caption label="Manut. Usuario" />
	        <grid fixedLayout="true">  
	         <rows>
	              <row>
				        Cod. Usuario: <textbox id="usuario" cols="10" />
				        
				        Empresa: <textbox id="empresa" cols="40" />
			       </row>
			       <row>
				        Senha: <textbox type="password" id="senha" cols="8" />
				        
				        Perfil: <combobox id="perfil" autodrop="true" >
				        			<comboitem  label="NIVEL 10" />
				        			<comboitem  label="NIVEL 8" />
				        			<comboitem  label="NIVEL 6" />
				        			<comboitem  label="NIVEL 4" />
				        			<comboitem  label="NIVEL 2" />
				        			<comboitem  label="NIVEL 0" /> 
				                </combobox>
			       </row>
			       
			       <row>	  
				       <button label="Icluir" width="36px" height="24px" onClick="usuarioClasse.add()" />
				       <button label="Alterar" width="46px" height="24px" onClick="usuarioClasse.update()" />
				       <button label="Excluir" width="46px" height="24px" onClick="usuarioClasse.delete()" />
				   </row>   
		       </rows>
	       </grid>
</groupbox>
    
    <separator/>
  
</window>
</zk>

gera o erro:


06/04/2010 11:40:20 org.zkoss.zk.ui.metainfo.Property assign:175
SEVERE: Failed to assign [type=submit] to <Button z_aj_11>
Method setType not found for class org.zkoss.zul.Button
06/04/2010 11:40:20 org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet zkLoader threw exception
org.zkoss.zk.ui.metainfo.PropertyNotFoundException: Method setType not found for class org.zkoss.zul.Button
	at org.zkoss.zk.ui.metainfo.Property.resolve(Property.java:190)
	at org.zkoss.zk.ui.metainfo.Property.assign0(Property.java:206)
	at org.zkoss.zk.ui.metainfo.Property.assign(Property.java:173)
	at org.zkoss.zk.ui.metainfo.ComponentInfo.applyProperties(ComponentInfo.java:781)
	at org.zkoss.zk.ui.impl.AbstractUiFactory.newComponent(AbstractUiFactory.java:93)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild0(UiEngineImpl.java:622)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild(UiEngineImpl.java:593)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate0(UiEngineImpl.java:537)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate(UiEngineImpl.java:504)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild0(UiEngineImpl.java:637)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild(UiEngineImpl.java:593)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate0(UiEngineImpl.java:537)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate(UiEngineImpl.java:504)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild0(UiEngineImpl.java:637)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild(UiEngineImpl.java:593)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate0(UiEngineImpl.java:537)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate(UiEngineImpl.java:504)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild0(UiEngineImpl.java:637)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild(UiEngineImpl.java:593)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate0(UiEngineImpl.java:537)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate(UiEngineImpl.java:504)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild0(UiEngineImpl.java:637)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild(UiEngineImpl.java:593)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate0(UiEngineImpl.java:537)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate(UiEngineImpl.java:504)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild0(UiEngineImpl.java:637)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild(UiEngineImpl.java:593)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate0(UiEngineImpl.java:537)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild(UiEngineImpl.java:569)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate0(UiEngineImpl.java:537)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate(UiEngineImpl.java:504)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execNewPage0(UiEngineImpl.java:365)
	at org.zkoss.zk.ui.impl.UiEngineImpl.execNewPage(UiEngineImpl.java:286)
	at org.zkoss.zk.ui.http.DHtmlLayoutServlet.process(DHtmlLayoutServlet.java:237)
	at org.zkoss.zk.ui.http.DHtmlLayoutServlet.doGet(DHtmlLayoutServlet.java:159)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:852)
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
	at java.lang.Thread.run(Unknown Source)

Alguém sabe o que pode ser esse erro ?

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