Javascript Error when I run Ajax tool kit calendar

Hi all,

I have issue with Ajax Toolkit in my project. When i run my webpage a javascript error is showing like

JavaScript runtime error: Unable to get property 'name' of undefined or null reference

Below is my code. Please review and let me know where i am missing.. I am facing this issue from couple of days ...

<%@ Page Title="" Language="C#" MasterPageFile="~/VirtualCRM.master" AutoEventWireup="true" CodeFile="Call.aspx.cs" Inherits="Call" %>

<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp" %>

<asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server">
    <style type="text/css">
        .style2
        {
            font-size: large;
            font-weight: bold;
        }
    </style>
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
    <p class="style2">Calls</p>
<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
    </asp:ToolkitScriptManager>
<table width="100%" frame="border">
<tr>
<td>
<asp:Label ID="lblSubject" runat="server" Text="Subject"></asp:Label>
<asp:Label ID="lblsubjct" runat="server" Text="*" ForeColor="Red"></asp:Label>
</td>
<td>
    
<asp:TextBox ID="txtSubject" runat="server"></asp:TextBox>
    <asp:RequiredFieldValidator ID="RequiredFieldValidatorSubject" runat="server" ErrorMessage="Enter Subject" ForeColor="Red" ControlToValidate="txtSubject"></asp:RequiredFieldValidator>
</td>
<td>
<asp:Label ID="lblStatus" runat="server" Text="Status"></asp:Label>
</td>
<td>
<asp:DropDownList ID="drpdwnStatus" runat="server">
<asp:ListItem>None</asp:ListItem>
<asp:ListItem>Planned</asp:ListItem>
<asp:ListItem>Held</asp:ListItem>
<asp:ListItem>Not Held</asp:ListItem>
<asp:ListItem>No Answered</asp:ListItem>
</asp:DropDownList>
</td>
</tr>
<tr>
<td>
<asp:Label ID="lblDatetime" runat="server" Text="Date & Time"></asp:Label>
<asp:Label ID="lblDate" runat="server" Text="*" ForeColor="Red"></asp:Label>
</td>
<td>
<asp:TextBox ID="txtdate" runat="server"></asp:TextBox>
<asp:ImageButton ID="imgPopup" ImageUrl="~/calendar-128.png" ImageAlign="Bottom"
        runat="server" Width="19px" />
    <asp:CalendarExtender ID="CalendarExtender1" runat="server" PopupButtonID="imgPopup" TargetControlID="txtdate" Format="dd/MM/yyyy">
    </asp:CalendarExtender>
    <asp:DropDownList ID="drpdwn1" runat="server">
    <asp:ListItem>01</asp:ListItem>
    <asp:ListItem>02</asp:ListItem>
    <asp:ListItem>03</asp:ListItem>
    <asp:ListItem>04</asp:ListItem>
    <asp:ListItem>05</asp:ListItem>
    <asp:ListItem>06</asp:ListItem>
    <asp:ListItem>07</asp:ListItem>
    <asp:ListItem>08</asp:ListItem>
    <asp:ListItem>09</asp:ListItem>
    <asp:ListItem>10</asp:ListItem>
    <asp:ListItem>11</asp:ListItem>
    <asp:ListItem>12</asp:ListItem>
    </asp:DropDownList>
    <asp:DropDownList ID="drpdwn2" runat="server">
    <asp:ListItem>00</asp:ListItem>
    <asp:ListItem>15</asp:ListItem>
    <asp:ListItem>30</asp:ListItem>
    <asp:ListItem>45</asp:ListItem>
    <asp:ListItem>60</asp:ListItem>
    </asp:DropDownList>
    <asp:DropDownList ID="drpdwn3" runat="server">
    <asp:ListItem>AM</asp:ListItem>
    <asp:ListItem>PM</asp:ListItem>
    </asp:DropDownList>
    <asp:RequiredFieldValidator ID="RequiredFieldValidatordate" runat="server" ErrorMessage="Select Date" ForeColor="Red" ControlToValidate="txtdate"></asp:RequiredFieldValidator>
    </td>
    <td>
   &nbsp;
    </td>
    <td>
     <asp:DropDownList ID="ddlTimeZone" runat="server" AutoPostBack="True"
        onselectedindexchanged="ddlTimeZone_SelectedIndexChanged"
        AppendDataBoundItems="true" >
            <asp:ListItem Text="Select a TimeZone" Value="Default value" />
    </asp:DropDownList>
    </td>
    </tr>
    <tr>
    <td>
    <asp:Label ID="lblDuration" runat="server" Text="Duration"></asp:Label>
    <asp:Label ID="Duration" runat="server" Text="*" ForeColor="Red"></asp:Label>
    </td>
    <td>
    <asp:TextBox ID="txtduration" runat="server"></asp:TextBox>
    <asp:DropDownList ID="drpdwndduration" runat="server">
    <asp:ListItem>00</asp:ListItem>
    <asp:ListItem>15</asp:ListItem>
    <asp:ListItem>30</asp:ListItem>
    <asp:ListItem>45</asp:ListItem>
    <asp:ListItem>60</asp:ListItem>
    </asp:DropDownList>
    <asp:Label ID="lbl" runat="server" Text="(hours/minutes)"></asp:Label>
        <asp:RequiredFieldValidator ID="RequiredFieldValidatorduration" runat="server" ErrorMessage="Enter Durationtime" ForeColor="Red" ControlToValidate="txtduration"></asp:RequiredFieldValidator>
    </td>
    <td>
    &nbsp;
    </td>
    <td>
    Local Time: <asp:Label ID="lblLocalTime" runat="server" Text=""></asp:Label>
    
    </td>
    </tr>
    <tr>
    <td>
    <asp:Label ID="lblDescription" runat="server" Text="Description"></asp:Label>
    </td>
    <td>
    <asp:TextBox ID="txtDescription" runat="server" TextMode="MultiLine" Height="102px"
            Width="266px"></asp:TextBox>
    </td>
    <td>
    &nbsp;
    </td>
    <td>
    Converted Time: <asp:Label ID="lblTimeZone" runat="server" Text=""></asp:Label>  
    </td>
    </tr>
    </table>
    <asp:Button ID="btnSave" runat="server" Text="Save"
    onclick="btnSave_Click" />
    &nbsp;&nbsp;
    <asp:Button ID="btnCancel" runat="server" Text="Cancel"
    onclick="btnCancel_Click" />
</asp:Content>

I hope someone can help me out from this issue.

Regards,

Laxman