The error explains everything. You need todefine the event method for OnRowDeleting
in markup:
<asp:GridView ID="gvorderlist" runat="server" CellPadding="4"
ForeColor="#333333" GridLines="None" AllowPaging="True" PageSize="5"
onpageindexchanging="gvorderlist_PageIndexChanging"
onrowcommand="gvorderlist_RowCommand" OnRowDeleting="gvorderlist_RowDeleting">
<AlternatingRowStyle BackColor="White" />
<Columns>
<asp:TemplateField HeaderText="Cancel Order" ShowHeader="False">
<ItemTemplate>
<asp:ImageButton ID="ImgbtnCancelOrder" runat="server" CausesValidation="false"
ImageUrl="~/images/cross.PNG" OnClientClick="Javascript: return confirm('Aap Chutiye hai');" CommandName="Delete"
CommandArgument="<%# ((GridViewRow) Container).RowIndex %>"/>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
And add an empty method in the code:
protected void gvorderlist_RowDeleting(object sender, GridViewDeleteEventArgs e)
{
// No need to implement code here
}