Exporting Excel is giving error on button click - asp.net

Question

I am implementing the functionality that on button click the data saved in the gridview should get exported on the button click, I implemented the functionality from here.
But I am getting error as Control 'mainContent_grdTeacherProfile' of type 'GridView' must be placed inside a form tag with runat=server at line
grdTeacherProfile.RenderControl(hw);
Please see the asps code of the gridview:-
<asp:GridView ID="grdTeacherProfile"
runat="server"
Width="100%"
border="1" Style="border: 1px solid #E5E5E5;"
CellPadding="3" FooterStyle-BackColor="#e3e3e3"
AutoGenerateColumns="false"
AllowPaging="true"
CssClass="hoverTable"
DataKeyNames="Id"
PageSize="4"
ShowFooter="false"
OnPreRender="PreRenderGrid"
HeaderStyle-CssClass="k-grid td"
OnDataBound="grdTeacherProfile_DataBound"
OnPageIndexChanging="grdTeacherProfile_PageIndexChanging"
OnRowDeleting="grdTeacherProfile_RowDeleting"
OnRowCommand="grdTeacherProfile_RowCommand"
EnableSortingAndPagingCallbacks="false"
EmptyDataText="No records found">
<AlternatingRowStyle CssClass="k-alt" />
<Columns>
<asp:TemplateField HeaderText="Select" ItemStyle-Width="5" >
<ItemTemplate>
<asp:CheckBox ID="chkDelete" runat="server" onClick="Check_Click(this)" />
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="first_name" HeaderText="First Name" ItemStyle-Width="30" />
<asp:BoundField DataField="last_name" HeaderText="Last Name" ItemStyle-Width="30" />
<asp:BoundField DataField="dob" HeaderText="Date of Birth" ItemStyle-Width="20" ApplyFormatInEditMode="true" DataFormatString="{0:d}" />
<asp:BoundField DataField="gender" HeaderText="Gender" ItemStyle-Width="20" />
<asp:BoundField DataField="designation" HeaderText="Designation" ItemStyle-Width="20" />
<asp:BoundField DataField="joining_date" HeaderText="Joining Date" ItemStyle-Width="20" ApplyFormatInEditMode="true" DataFormatString="{0:d}" />
<asp:BoundField DataField="leaving_date" HeaderText="Leaving Date" ItemStyle-Width="20" ApplyFormatInEditMode="true" DataFormatString="{0:d}" />
<asp:BoundField DataField="active" HeaderText="Active" ItemStyle-Width="25" />
<asp:TemplateField HeaderText="Action" HeaderStyle-Width="5%">
<ItemTemplate>
<asp:ImageButton ID="btnEdit" AlternateText="Edit" ImageUrl="~/images/edit.png" runat="server" Width="15" Height="15" CommandName="eEdit" CommandArgument='<%# Eval("Id") %>' CausesValidation="false" />
<asp:ImageButton ID="btnDelete" AlternateText="Delete" ImageUrl="~/images/delete.png" runat="server" Width="15" Height="15" CommandName="Delete" CommandArgument='<%# Eval("Id") %>' CausesValidation="false" OnClientClick="return confirm('Are you sure you want to delete this record?')" />
</ItemTemplate>
</asp:TemplateField>
</Columns>
<PagerStyle ForeColor="#e3e3e3"
BackColor="#e3e3e3" CssClass="grid-pagi" />
<PagerTemplate>
<table runat="server" id="testTable1" style="width: 100%" class="hoverTable_tbl">
<tr>
<td class="col-md-4 pull-left">
<asp:Label ID="MessageLabel"
Text="Select a page:"
runat="server" />
<asp:LinkButton ID="FirstLB" runat="server" CommandName="Page" CommandArgument="First" ToolTip="First" CssClass="btn-pager btn-default"><<</asp:LinkButton>
<asp:LinkButton ID="PrevLB" runat="server" CommandName="Page" CommandArgument="Prev" ToolTip="Previous" CssClass="btn-pager btn-default"><</asp:LinkButton>
<asp:DropDownList runat="server" ID="PageDropDownList" AutoPostBack="true" EnableViewState="true" OnSelectedIndexChanged="PageDropDownList_SelectedIndexChanged" CssClass="selectpicker form-control-drp"></asp:DropDownList>
<asp:LinkButton ID="NextLB" runat="server" CommandName="Page" CommandArgument="Next" ToolTip="Next" CssClass="btn-pager btn-default">></asp:LinkButton>
<asp:LinkButton ID="LastLB" runat="server" CommandName="Page" CommandArgument="Last" ToolTip="Last" CssClass="btn-pager btn-default">>></asp:LinkButton>
</td>
<td class="col-md-3">
<div>
<div class="pull-left"><asp:Label ID="PageSizeLabel" CssClass="page-size" runat="server" Text="Select Page Size: "></asp:Label>
<asp:DropDownList ID="ddlPageSize" runat="server" OnSelectedIndexChanged="ddlPageSize_SelectedIndexChanged" AutoPostBack="true" CssClass="selectpicker form-control-drp">
<%-- <asp:ListItem Value="0" Text="0" />--%>
<asp:ListItem Value="1" Text="1" />
<asp:ListItem Value="2" Text="2" />
<asp:ListItem Value="3" Text="3" />
</asp:DropDownList>
</div>
<div>
<asp:Label ID="CurrentPageLabel" CssClass="view" runat="server" />
</div>
</div>
</td>
</tr>
</table>
</PagerTemplate>
<RowStyle />
</asp:GridView>

Answer 1

Exporting GridView to Excel is easier using a 3rd party like iTextSharp.
If you want to know how I make it work, you can check this sample code:
http://dotnetfrommanila.blogspot.com/2013/04/convert-gridview-to-excel-in-c.html
I hope it could help you.

Answer 2

I got it done on my own,
actually I forgot to add the code below and EnableEventValidation="false".
The code was:-
public override void VerifyRenderingInServerForm(Control control)
{
/* Verifies that the control is rendered */
}
and it worked.!!