Please try this
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Date.aspx.cs" Inherits="page1" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp" %>
<html>
<head id="Head1" runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<asp:ToolkitScriptManager ID="tool1" runat="server">
</asp:ToolkitScriptManager>
<table>
<tr>
<td>
Empno:
</td>
<td style="margin-left: 40px">
<asp:TextBox ID="TxtEmpno" onkeypress="return isNumberKey(event);" runat="server"
Width="300px" MaxLength="6"></asp:TextBox>
</td>
<td style="margin-left: 40px">
</td>
</tr>
<tr>
<td>
From Date :
</td>
<td>
<asp:TextBox ID="TxtDateFrom" runat="server" CssClass="txtbox"></asp:TextBox>
<asp:ImageButton ID="Img_DateFrom" runat="server" ImageUrl="~/Images/1.jpg" AlternateText="Click here to display the calender"
align="center" Height="25px" Width="43px" />
</td>
<td>
<asp:MaskedEditExtender ID="MaskedEditExtender1" runat="server" TargetControlID="TxtDateFrom"
MaskType="Date" Mask="99/99/9999" MessageValidatorTip="true" InputDirection="LeftToRight"
ErrorTooltipEnabled="True" AcceptNegative="None">
</asp:MaskedEditExtender>
<asp:MaskedEditValidator ID="MaskedEditValidator1" runat="server" ControlExtender="MaskedEditExtender1"
ControlToValidate="TxtDateFrom" IsValidEmpty="true" ForeColor="Red" EmptyValueMessage="Enter Date Value"
InvalidValueMessage="Date Fromat should be (MM/dd/yyyy)." InvalidValueBlurredMessage="Date Format (MM/dd/yyyy)."
EmptyValueBlurredText="*" Display="None">
</asp:MaskedEditValidator>
<asp:CalendarExtender ID="CalendarExtender1" Format="MM/dd/yyyy" runat="server" TargetControlID="TxtDateFrom"
PopupButtonID="Img_DateFrom" />
<asp:ValidatorCalloutExtender ID="VCEField1" runat="server" TargetControlID="MaskedEditValidator1">
</asp:ValidatorCalloutExtender>
<asp:CompareValidator ID="CompareValidator1" runat="server" ErrorMessage="End date must be greater than start date"
Display="None" ControlToCompare="TxtDateFrom" ControlToValidate="TxtDateTo" Operator="GreaterThanEqual"
Type="Date"></asp:CompareValidator>
<asp:ValidatorCalloutExtender ID="ValidatorCalloutExtender2" runat="server" TargetControlID="CompareValidator1">
</asp:ValidatorCalloutExtender>
</td>
</tr>
<tr>
<td>
To Date :
</td>
<td>
<asp:TextBox ID="TxtDateTo" runat="server" CssClass="txtbox"></asp:TextBox>
<asp:ImageButton ID="Img_DateTo" runat="server" ImageUrl="~/Images/1.jpg" AlternateText="Click here to display the calender"
align="center" Height="26px" Style="margin-top: 0px" Width="43px" />
</td>
<td>
<asp:MaskedEditExtender ID="MaskedEditExtender2" runat="server" TargetControlID="TxtDateTo"
MaskType="Date" Mask="99/99/9999" MessageValidatorTip="true" InputDirection="RightToLeft"
AcceptNegative="None" ErrorTooltipEnabled="True">
</asp:MaskedEditExtender>
<asp:MaskedEditValidator ID="MaskedEditValidator2" runat="server" ControlExtender="MaskedEditExtender2"
ControlToValidate="TxtDateTo" IsValidEmpty="true" ForeColor="Red" EmptyValueMessage="Enter Date Value"
InvalidValueMessage="Date Fromat should be (MM/dd/yyyy)." Display="None" InvalidValueBlurredMessage="(MM/dd/yyyy)"
EmptyValueBlurredText="*">
</asp:MaskedEditValidator>
<asp:CalendarExtender ID="CalendarExtender2" Format="MM/dd/yyyy" runat="server" TargetControlID="TxtDateTo"
PopupButtonID="Img_DateTo">
</asp:CalendarExtender>
<asp:ValidatorCalloutExtender ID="ValidatorCalloutExtender1" runat="server" TargetControlID="MaskedEditValidator2">
</asp:ValidatorCalloutExtender>
</td>
</tr>
<tr>
<td>
Time :
</td>
<td>
<asp:TextBox ID="txttime" runat="server"></asp:TextBox>
</td>
<td>
<asp:MaskedEditExtender ID="MaskedEditExtender3" runat="server" TargetControlID="txttime"
MaskType="Time" Mask="99:99:99" MessageValidatorTip="true" InputDirection="RightToLeft"
AcceptNegative="None" ErrorTooltipEnabled="True" AcceptAMPM="true">
</asp:MaskedEditExtender>
</td>
<td>
<asp:MaskedEditValidator ID="MaskedEditValidator3" runat="server" ControlExtender="MaskedEditExtender3"
ControlToValidate="txttime" IsValidEmpty="true" ForeColor="Red" EmptyValueMessage="Enter Date Value"
InvalidValueMessage="Time fomat wrong." Display="None" InvalidValueBlurredMessage="wrong"
EmptyValueBlurredText="***">
</asp:MaskedEditValidator>
</td>
<td>
<asp:Label ID="label2" runat="server"></asp:Label>
</td>
</tr>
<tr>
<td>
</td>
<td>
</td>
<td>
<asp:Button ID="Button1" runat="server" Text="Submit" onclick="Button1_Click" />
</td>
</tr>
</table>
</form>
</body>
</html>