I am posting the aspx code here. I have tried it already the above suggestion but still the same problem.
<html>
<head id="Head1" runat="server">
<title>Schedule Exam</title>
<style type="text/css">
.style2
{
width: 140px;
}
.style3
{
width: 142px;
}
.style7
{
width: 241px;
}
</style>
</head>
<body>
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<table style="border-left: thin groove olive; border-right-style: groove; border-right-width: thin; border-top-style: groove; border-top-width: thin; border-bottom-style: groove; border-bottom-width: thin;">
<tr>
<td colspan="3"
style="border: thin double #808000; font-weight:700; text-align: center; background-color: olive; color:White;">
<asp:Label ID="lblHeading" runat="server" Font-Names="Tahoma" Font-Size="Small"
Text="Schedule an Event"></asp:Label>
</td>
</tr>
<tr>
<td colspan="3">
</td>
</tr>
<tr>
<td align="center" colspan="3" >
<asp:Label ID="lblStartTime" runat="server" Font-Bold="False"
Font-Names="Tahoma" Font-Size="Small" Text="Start Time"></asp:Label>
<asp:TextBox ID="txtStartDate" runat="server" Width="80px" Font-Names="Tahoma"
Font-Size="Small" Height="19px"></asp:TextBox>
<asp:Image ID="imgCalendar1" runat="server" ImageUrl="~/Images/Calendar_scheduleHS.png" />
<cc1:CalendarExtender ID="clnExtender1" runat="server" TargetControlID="txtStartDate"
PopupButtonID="imgCalendar1"> </cc1:CalendarExtender>
<cc2:TimeSelector ID="tsStartTime" runat="server" AllowSecondEditing="False"
MinuteIncrement="10" Height="20px" Width="140px" />
</td>
</tr>
<tr>
<td colspan="3" style="text-align:center;">
<asp:Label ID="lblStartTimeError" runat="server" Font-Bold="True"
Font-Names="Tahoma" Font-Size="7pt" ForeColor="Red" Visible="False"></asp:Label>
</td>
</tr>
<tr>
<td align="center" colspan="3">
<asp:Label ID="lblEndTime" runat="server" Font-Bold="False" Font-Names="Tahoma"
Font-Size="Small" Text="End Time" ></asp:Label>
<asp:TextBox ID="txtEndDate" runat="server" Width="80px"
Font-Names="Tahoma" Font-Size="Small" Height="19px"></asp:TextBox>
<asp:Image ID="imgCalendar2" runat="server" ImageUrl="~/Images/Calendar_scheduleHS.png" />
<cc1:CalendarExtender ID="clnExtendar2" runat="server" TargetControlID="txtEndDate"
PopupButtonID="imgCalendar2"> </cc1:CalendarExtender>
<cc2:TimeSelector ID="tsEndTime" runat="server" AllowSecondEditing="false"
MinuteIncrement="10" Height="20px" Width="140px" />
</td>
</tr>
<tr>
<td colspan="3" style="text-align:center;">
<asp:Label ID="lblEndTimeError" runat="server" Font-Bold="True"
Font-Names="Tahoma" Font-Size="7pt" ForeColor="Red"
Text="End time must be greater than start time" Visible="False"></asp:Label>
</td>
</tr>
<tr>
<td align="center" colspan="3">
<asp:LinkButton ID="btnResources" runat="server" Font-Bold="True"
Font-Names="Tahoma" Font-Size="9pt" ForeColor="Olive"
onclick="btnResources_Click">Set Time</asp:LinkButton>
</td>
</tr>
<tr>
<td align="center" colspan="3">
</td>
</tr>
<tr>
<td align="center" colspan="3">
<asp:Label ID="lblEvent" runat="server" Font-Bold="False" Font-Names="Tahoma"
Font-Size="Small" Text="Event" Visible="false"></asp:Label>
<asp

ropDownList ID="ddlEvent" runat="server" Height="22px"
Font-Names="Tahoma" Font-Size="Small"
onselectedindexchanged="ddlEvent_SelectedIndexChanged"
AutoPostBack="True" Width="144px" Visible="false">
<asp:ListItem></asp:ListItem>
<asp:ListItem>Exam</asp:ListItem>
<asp:ListItem>Meeting</asp:ListItem>
</asp

ropDownList>
</td>
</tr>
<tr>
<td align="center" colspan="3">
<asp:Label ID="lblProtocols" runat="server" Text="Protocol"
Visible="False" Font-Names="Tahoma" Font-Size="Small"></asp:Label> <asp

ropDownList
ID="ddlProtocols" runat="server" Height="22px"
Width="144px" Visible= "False" AutoPostBack="True"
onselectedindexchanged="ddlProtocols_SelectedIndexChanged"
Font-Names="Tahoma" Font-Size="Small">
</asp

ropDownList>
</td>
</tr>
<tr>
<td colspan="3" align="center">
<asp:UpdatePanel ID="selectionsPanel" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<table>
<tr>
<td align="right">
<asp:Label ID="lblClinicID" runat="server" Font-Bold="False"
Font-Names="Tahoma" Font-Size="Small" Text="Clinic ID" visible="false"></asp:Label>
</td>
<td align="left" colspan="2">
<asp:TextBox ID="txtClinicID" runat="server" AutoPostBack="True"
CausesValidation="True" Font-Names="Tahoma" Font-Size="Small" Height="18px"
ontextchanged="txtClinicID_TextChanged" visible="false" Width="132px"></asp:TextBox>
<cc1:FilteredTextBoxExtender ID="txtClinicID_FilteredTextBoxExtender"
runat="server" Enabled="True" FilterType="Numbers"
TargetControlID="txtClinicID">
</cc1:FilteredTextBoxExtender>
<asp:RequiredFieldValidator ID="valClinicID" runat="server"
ControlToValidate="txtClinicID" Display="Dynamic" ErrorMessage="Required"
Font-Bold="True" Font-Names="Tahoma" Font-Size="7pt" SetFocusOnError="True"
Visible="False"></asp:RequiredFieldValidator>
<%--<cc1:ValidatorCalloutExtender ID="valClinicIDE"
runat="server" TargetControlID="valClinicID">
</cc1:ValidatorCalloutExtender>--%>
<asp:RangeValidator ID="rangeVldClinicID" runat="server"
ControlToValidate="txtClinicID" ErrorMessage="Invalid Number" Font-Bold="True"
Font-Names="Tahoma" Font-Size="Smaller" MaximumValue="999999999"
MinimumValue="0" Type="Double"></asp:RangeValidator>
</td>
</tr>
<tr>
<td align="right">
<asp:Label ID="lblRooms" runat="server" Font-Bold="False" Font-Names="Tahoma"
Font-Size="Small" Text="Room" visible="false"></asp:Label>
</td>
<td colspan="2" align="left">
<asp

ropDownList ID="ddlRooms" runat="server" DataTextField="room_name"
DataValueField="room_id" Font-Names="Tahoma" Font-Size="Small" Height="24px"
visible="false" Width="137px" AutoPostBack="True"
onselectedindexchanged="ddlRooms_SelectedIndexChanged"></asp

ropDownList>
<asp:Label ID="valRoom" runat="server"
Text="No room available" visible="False" Font-Bold="True"
Font-Names="Tahoma" Font-Size="7pt" ForeColor="Red"></asp:Label>
</td>
</tr>
<tr>
<td align="right">
<asp:Label ID="lblEquipment" runat="server" Font-Bold="False"
Font-Names="Tahoma" Font-Size="Small" Text="Equipment" visible="false"></asp:Label>
</td>
<td colspan="2" align="left">
<asp

ropDownList ID="ddlEquipment" runat="server" DataTextField="equip_name"
DataValueField="equip_id" Font-Names="Tahoma" Font-Size="Small" Height="24px"
visible="false" Width="137px" AutoPostBack="True"
onselectedindexchanged="ddlEquipment_SelectedIndexChanged"> </asp

ropDownList>
<asp:Label ID="valEquip" runat="server"
Text="No equip available" visible="False" Font-Bold="True"
Font-Names="tahoma" Font-Size="7pt" ForeColor="Red"></asp:Label>
</td>
</tr>
<tr>
<td>
<asp:Label ID="lblAvailableWorkers" runat="server" Font-Bold="False"
Font-Names="Tahoma" Font-Size="Small" Text="Available Workers" visible="false"></asp:Label>
</td>
<td>
</td>
<td>
<asp:Label ID="lblSelectedWorkers" runat="server" Font-Bold="False"
Font-Names="Tahoma" Font-Size="Small" Text="Selected Workers" visible="false"></asp:Label>
</td>
</tr>
<tr>
<td align="right" rowspan="2">
<asp:ListBox ID="lstAvailableWorkers" runat="server" visible="false" AutoPostBack="True"
DataTextField="name" Font-Names="Tahoma" Font-Size="Small" Height="70px"
Rows="100" Width="191px" DataValueField="pid">
<asp:ListItem></asp:ListItem>
</asp:ListBox>
</td>
<td>
<asp:Button ID="btnEmployeeRight" runat="server" visible="False"
onclick="btnEmployeeRight_Click" Text="-->" Width="35px" OnClientClick="return true;" />
</td>
<td align="left" rowspan="2">
<asp:ListBox ID="lstSelectedWorkers" runat="server" AutoPostBack="True"
Font-Names="Tahoma" Font-Size="Small" Height="70px" Rows="100" visible="false"
Width="189px" DataTextField="name" DataValueField="pid"
style="margin-left: 0px"></asp:ListBox>
</td>
</tr>
<tr>
<td>
<asp:Button ID="btnEmployeeLeft" runat="server" onclick="btnEmployeeLeft_Click"
Text="<--" Width="35px" visible="false"/>
</td>
</tr>
<tr>
<td colspan="3" style="text-align:center;">
<asp:Label ID="lblWorkers" runat="server" Font-Bold="True" Font-Names="Tahoma"
ForeColor="Red" font-size="7pt" Visible="False" ></asp:Label>
</td>
</tr>
<tr>
<td style="text-align:right;">
<asp:Label ID="lblDescription" runat="server" Font-Names="Tahoma"
Font-Size="Small" Text="Event Description" Visible="False"></asp:Label>
</td>
<td colspan="2" style="text-align:left;">
<asp:TextBox ID="txtEventDescription" runat="server" Height="53px"
MaxLength="100" style="margin-left: 0px" TextMode="MultiLine" Visible="False"
Width="180px"></asp:TextBox>
<asp:RegularExpressionValidator ID="valDescription" runat="server"
ControlToValidate="txtEventDescription" Display="Dynamic"
ErrorMessage="Invalid Characters" Font-Bold="True" Font-Names="Tahoma"
Font-Size="7pt" SetFocusOnError="True"
ValidationExpression="[a-zA-z0-9\t\s,;:&.'_-]*$" Visible="False"></asp:RegularExpressionValidator>
</td>
</tr>
<tr>
<td colspan="3" style="text-align:center;">
<asp:Label ID="lblMessage" runat="server" Font-Bold="True" Font-Names="Tahoma"
ForeColor="Red" font-size="7pt" Visible="False" ></asp:Label>
</td>
</tr>
</table>
</ContentTemplate>
<Triggers>
<asp

ostBackTrigger ControlID="btnEmployeeRight" />
<asp

ostBackTrigger ControlID="txtClinicID" />
<asp

ostBackTrigger ControlID="ddlRooms" />
<asp

ostBackTrigger ControlID="ddlEquipment" />
</Triggers>
</asp:UpdatePanel>
</td>
</tr>
<tr>
<td align="center" class="style2">
</td>
<td align="center" class="style3">
</td>
<td align="center" class="style7">
</td>
</tr>
<tr>
<td align="center">
<asp:Button ID="btnCancel" runat="server" align="center" Text="Cancel" Width="78px"
Font-Bold="False" Font-Names="Tahoma" Font-Size="Small" Height="30px"
onclientclick="window.close();" onclick="btnCancel_Click" />
</td>
<td align="center">
<asp:Button ID="btnClear" runat="server" align="center" Text="Clear" Width="78px"
Font-Bold="False" Font-Names="Tahoma" Font-Size="Small" Height="30px"
onclick="btnClear_Click"
onclientclick="ValidatorEnable(valClinicID, false);"/>
</td>
<td align="center">
<asp:Button ID="btnSave" runat="server" align="center" Text="Save" Width="78px"
Font-Bold="False" Font-Names="Tahoma" Font-Size="Small" Height="30px"
onclick="btnSave_Click" Enabled="False" UseSubmitBehavior="true" />
</td>
</tr>
<tr>
<td colspan="3" align="center">
<asp:ObjectDataSource ID="objdsProtocols" runat="server"
OldValuesParameterFormatString="original_{0}" SelectMethod="GetExamProtocols"
TypeName="IUSO.AppCode.ExamProtocolsDSTableAdapters.ProtocolTableAdapter">
</asp:ObjectDataSource>
</td>
</tr>
</table>
</form>
</body></html>