ajax的AsyncPostBackTrigger没效果

            <div id="div6" runat="server" style= "height:auto;width:auto; text-align: left;">
            <asp:UpdatePanel ID="UpdatePanel2" runat="server" UpdateMode="Conditional">
            <ContentTemplate>
                          <asp:TextBox ID="tbRegisterID0" runat="server" Width="58px" 
                        ontextchanged="tbRegisterID_TextChanged" TabIndex="2"                 AutoPostBack="True"></asp:TextBox>     <asp:TextBox ID="tbPatientID" runat="server"
                        ontextchanged="tbPatientID_TextChanged" AutoPostBack="True" TabIndex="3"></asp:TextBox>
            
           </ContentTemplate>
             </asp:UpdatePanel>                                              
             </div>            <div id="div4" runat="server" style= "height:350px;width:auto; text-align: left;">
          <asp:UpdatePanel ID="UpdatePanel4" runat="server" UpdateMode="Conditional">
            <Triggers>
                   <asp:PostBackTrigger ControlID="btnNext" />
                  <asp:AsyncPostBackTrigger ControlID="tbRegisterID0" />
                   <asp:AsyncPostBackTrigger ControlID="tbPatientID" />
            </Triggers>
   <ContentTemplate>
               <asp:GridView ID="gvKindList" Runat="server" >
                ......
                       </ContentTemplate>
             </asp:UpdatePanel>                                              
             </div>为什么tbRegisterID0的TextChanged事件不会触发GridView 的更新