GWT面板类型的问题

我目前正在尝试为GWT应用程序创建一个符合w3c标准的HTML/CSS接口,这很大程度上取决于在正确的位置使用正确类型的面板,而不是使用嵌套的水平和垂直面板在UI中写出表。

我在GWT完全是一个n00b,不明白为什么替换下面代码中的顶部垂直面板会导致应用程序停止工作。任何用户界面编码资源,任何类型的建议将非常感谢。

<g:VerticalPanel>
    <g:FormPanel ui:field="loginFormPanel" action="/cms/j_acegi_security_check.rpc" >
      <g:HTMLPanel>     

          <g:Label ui:field="signinLabel" styleName="{style.signinStyle}">
            <ui:msg key="signInText">Welcome to Perform CMS</ui:msg>
          </g:Label> 



          <g:Label ui:field="emailLabel" styleName="{style.loginFontStyle}">
            <ui:msg key="emailAddress">Email adress</ui:msg>
            address
          </g:Label>  

            <g:TextBox ui:field="email" name="j_username" styleName="{style.loginTextBoxStyle}"/>

            <g:Label styleName="{style.fontStyle}" ui:field="usernameError"/>

          <g:Label ui:field="passwordLabel" styleName="{style.loginFontStyle}">
            <ui:msg key="password">Password</ui:msg>
          </g:Label>         

            <g:PasswordTextBox ui:field="password" name="j_password" styleName="{style.loginTextBoxStyle}"/>

            <g:Label styleName="{style.fontStyle}" ui:field="passwordError"/>


        <g:HTMLPanel ui:field="submitPanel">
            <g:HTMLPanel ui:field="submitButtonPanel" styleName="{style.buttonPanelStyle}">
              <g:Image url="/cms/images/new_button_search_left.png" styleName="{style.image}"></g:Image>
              <g:Label ui:field="signIn" styleName="{style.submitLabelStyle}">
                <ui:msg key="signIn">Sign in</ui:msg>
              </g:Label>
              <g:SubmitButton styleName="{style.hide}">Submit</g:SubmitButton> 
              <g:Image url="/cms/images/new_button_search_right.png" styleName="{style.image}"></g:Image>
            </g:HTMLPanel>
        </g:HTMLPanel>


        <g:HTMLPanel ui:field="submitErrorsPanel" styleName="{style.submitErrorPanel}">

          <g:Label styleName="{style.fontStyle}" ui:field="submitErrorMessages"/>
        </g:HTMLPanel>


      </g:HTMLPanel>
    </g:FormPanel> 
    <g:HTMLPanel ui:field="loginSuccessPanel" styleName="{style.hide}">
      <g:Label styleName="{style.fontStyle}" ui:field="loginSuccessMessageLabel"/>
   </g:HTMLPanel>
  </g:VerticalPanel>