让superValidator的一个问题给难住了

用户名和密码为必填项,参考:<table cellpadding="0" cellspacing="0" style="margin-top: 10px; font-size: small;">
    <tr style="height: 100px;">
        <td colspan="2">
            <img src="Resources/LoginImages/booking_title.png" alt=""  />
        </td>
    </tr>
    <tr style="height: 20px;">
        <td colspan="2">
            <strong style="color: White; font-family: 微软雅黑; font-size: 14px;">LOGIN NAME</strong>
        </td>
    </tr>
    <tr style="height: 70px; vertical-align: top;">
        <td>
            <asp:TextBox runat="server" ID="txt_LoginName" CssClass="inputText" Width="280px"
                Height="23" AutoCompleteType="Disabled"></asp:TextBox>
        </td>
        <td style="padding-left: 10px;">
            <asp:RequiredFieldValidator CssClass="validate" ID="RequiredFieldValidator1" ErrorMessage="請輸入用戶名稱."
                ControlToValidate="txt_LoginName" runat="server" />
        </td>
    </tr>
    <tr style="height: 20px; vertical-align: bottom;">
        <td colspan="2">
            <strong style="color: White; font-family: 微软雅黑; font-size: 14px;">PASSWORD</strong>
        </td>
    </tr>
    <tr style="height: 40px; vertical-align: top;">
        <td align="center">
            <asp:TextBox runat="server" ID="txt_Password" Width="280px" Height="23" CssClass="inputText"
                TextMode="Password" AutoCompleteType="Disabled"></asp:TextBox>
        </td>
        <td style="padding-left: 10px;">
            <asp:RequiredFieldValidator ID="RequiredFieldValidator2" CssClass="validate" ErrorMessage="請輸入密碼."
                ControlToValidate="txt_Password" runat="server" />
        </td>
    </tr>
    <tr style="height: 90px;">
        <td colspan="2">
            <input id="btn_Login" type="image" src="Resources/LoginImages/login_btn.png" onclick="onClickLogin();return false;" />
            
        </td>
    </tr>
</table>