Help me how to clear error

Delivery Date :		Open the calendar popup.

            <asp:CommandField HeaderText="Delete" ShowDeleteButton="True" />
        
        <pagerstyle backcolor="#2461BF" forecolor="White" horizontalalign="Center" />
        <SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" />
        <HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
        <editrowstyle backcolor="#2461BF" />
        <alternatingrowstyle backcolor="White" />
        <emptydatatemplate>
            No Record
        </emptydatatemplate>
                    
         <br />
         <br />
         <tr><td class="style4">
              </td>
             <td class="style1">
                  </td>
             <td class="style5">
                  </td>
             </tr>
         
        <tr><td class="style6">Size :</td><td class="style7" colspan="2">
            <asp:DropDownList ID="cmbSize" runat="server" AutoPostBack="True" 
                        onselectedindexchanged="cmbSize_SelectedIndexChanged" 
                Height="26px" Width="128px">
            
        </td></tr>
         
        <tr><td class="style4">Amount :</td><td class="style1" colspan="2">
                        <asp:TextBox ID="txtAmt" runat="server" 
                        >
        </td></tr><tr><td class="style4">Extra Copies :</td><td class="style1">
                colspan="2">
            <asp:TextBox ID="txtNoofcopies" runat="server"  AutoPostBack="true"
                      ></td>
            </tr>
            <tr><td class="style4"> Extra Copy Amount :</td><td class="style1" colspan="2">
                        <asp:TextBox ID="TextBox1" runat="server" AutoPostBack="true" ontextchanged="TextBox1_TextChanged">
                        </td>
            <tr><td class="style4">
                Total</td><td class="style1" colspan="2">
            <asp:TextBox ID="txtTot"  runat="server"  AutoPostBack="true">
                        </td>
            <tr><td class="style4">
                <asp:Label ID="Label3" runat="server" Text="Lamination">
                </td><td class="style1" colspan="2">
                        <asp:DropDownList ID="Ddl" runat="server" Height="26px" Width="128px">
                                     
                        </td><tr>
        <td class="style4">
                <asp:Label ID="Label4" runat="server" Text="Lamination Amount">
                </td>
        <td class="style1" colspan="2">
                        <asp:TextBox ID="txtlami" runat="server" AutoPostBack="true" 
                            ontextchanged="txtlami_TextChanged" >
                        </td></tr>
            <tr><td class="style4"><asp:Label ID="Label1" runat="server" Text="Grand Total : " Font-Bold="true" Font-Size="Medium" 

>
                </td>
                <td class="style1" colspan="2">
                    <asp:TextBox ID="txtgrandtot" runat="server"  AutoPostBack="true"
                       >
                </td>
                <td>
                     </td></tr>
            <tr><td class="style4">
                <asp:Label ID="Label2" runat="server" Text="Paid Amount">
                </td>
                <td class="style1" colspan="2">
             <asp:TextBox ID="txtPaid" runat="server" ontextchanged="txtPaid_TextChanged"></td>
                <td>
                     </td></tr>
            <tr><td class="style4">Balance</td>
                <td class="style1" colspan="2">
                    <asp:TextBox ID="txtbalance" runat="server" 
                       >
                        </td>
                <td>
                     </td></tr>
            <tr><td class="style4">
                <asp:Button ID="btnAdd" runat="server" Text="Add" onclick="btnAdd_Click" /><asp:Button ID="btnSave" runat="server" Text="Save" onclick="btnSave_Click" />
                    <asp:Button ID="btnClear" runat="server" Text="Clear" 
            onclick="btnClear_Click" /></td>
                <td class="style1" colspan="2"> </td>
                <td>
                     </td></tr>
             
         <br />
            <asp:ImageButton ID="imgPrint" runat="server" ImageUrl="~/images/print.jpg" 
            onclick="imgPrint_Click" />
<br />
 
              
    <asp:Label ID="lblError" runat="server" Text="">
        
        


<%-- 
<script type="text/javascript">
        function ToggleCalendar()
        {
            var pnlCalendar = self.document.getElementById('pnlCalendar');
            if (pnlCalendar.style.display == 'none')
            {
                ShowHideCalendar(true);
            }
            else
            {
                ShowHideCalendar(false);
            }
        }
        function ShowHideCalendar(CanShow)
        {
            var pnlCalendar = self.document.getElementById('pnlCalendar');
            if (CanShow==true)
            {
                pnlCalendar.style.display = "block";
                var t = setTimeout("ShowHideCalendar(false)", 5000);
            }
            else
            {
                pnlCalendar.style.display = "none";
            }
        
        }
    </script>
    
      


    <style type="text/css">
        .style1
        {
            width: 347px;
        }
        .style2
        {
            width: 60px;
        }
    </style>
    --%>
   
      
  
  <asp:Content ID="Content1" runat="server" contentplaceholderid="head">

      <style type="text/css">
          .style1
          {
              width: 476px;
              text-align: left;
          }
          .style2
          {
              text-align: center;
          }
          .style4
          {
              text-align: right;
              width: 445px;
          }
          .style5
          {
              width: 85px;
              text-align: left;
          }
          .style6
          {
              text-align: right;
              width: 445px;
              height: 22px;
          }
          .style7
          {
              width: 476px;
              text-align: left;
              height: 22px;
          }
      </style>



  </tr></tr></tr>