This is my code
<asp:updatepanel id="UPDPanel1" runat="server" updatemode="Always" childrenastriggers="true">
<%-- <triggers> <asp:asyncpostbacktrigger controlid="DrpFunctionality" eventname="SelectedIndexChanged">
--%>
<contenttemplate>
<%--<asp:panel id="panel1" runat="server" visible="true">--%>
<asp:dropdownlist id="DrpFunctionality" enableviewstate="true" clientidmode="Inherit" runat="server" cssclass="inp" width="100%" onselectedindexchanged="DrpFunctionality_SelectedIndexChanged" autopostback="true">
<asp:requiredfieldvalidator id="ReqFVFunctionality" setfocusonerror="true" forecolor="Red" runat="server" initialvalue="Select Functionality" controltovalidate="DrpFunctionality" errormessage="Functionality Required" validationgroup="Submit" display="Dynamic">
<asp:dropdownlist id="DrpSubFunctionality" enableviewstate="true" clientidmode="Inherit" runat="server" cssclass="inp" width="100%" autopostback="true">
<asp:requiredfieldvalidator id="ReqFVFun" setfocusonerror="true" forecolor="Red" runat="server" initialvalue="Select Sub-Functionality" controltovalidate="DrpSubFunctionality" errormessage="Sub-Functionality Required" validationgroup="Submit" display="Dynamic">
<asp:dropdownlist id="DrpEndUse" runat="server" enableviewstate="true" cssclass="inp" width="100%" onselectedindexchanged="DrpEndUse_SelectedIndexChanged" autopostback="true">
<asp:requiredfieldvalidator id="ReqFVEndUse" setfocusonerror="true" forecolor="Red" runat="server" initialvalue="Select End Use" controltovalidate="DrpEndUse" errormessage="End Use Required" validationgroup="Submit" display="Dynamic">
<asp:dropdownlist id="DrpSubEndUse" runat="server" enableviewstate="true" cssclass="inp" width="100%" autopostback="true">
<asp:requiredfieldvalidator id="ReqFVSubEndUse" setfocusonerror="true" forecolor="Red" runat="server" initialvalue="Select Sub-End Use" controltovalidate="DrpSubEndUse" errormessage="Sub-End Use Required" validationgroup="Submit" display="Dynamic">
<asp:dropdownlist id="DrpSolution" enableviewstate="true" runat="server" cssclass="inp" width="100%" onselectedindexchanged="DrpSolution_SelectedIndexChanged" autopostback="true">
<asp:requiredfieldvalidator id="ReqFVSolution" setfocusonerror="true" forecolor="Red" runat="server" initialvalue="Select Solution" controltovalidate="DrpSolution" errormessage="Solution Required" validationgroup="Submit" display="Dynamic">
<asp:dropdownlist id="DrpSubSolution" enableviewstate="true" runat="server" cssclass="inp" width="100%">
<asp:requiredfieldvalidator id="ReqFVSubSol" setfocusonerror="true" forecolor="Red" runat="server" initialvalue="Select Sub-Solution" controltovalidate="DrpSubSolution" errormessage="Sub-Solution Required" validationgroup="Submit" display="Dynamic">
<%----%>