A page can have only one server-side Form tag. [Resolved]

Showing Error as: A page can have only one server-side Form tag.
Let me know where i made the mistake.

Expecting your valuable reply

<%@ Page Language="vb" AutoEventWireup="false" MasterPageFile="~/BasicTutor.Master" CodeBehind="HandlingServerControlEvents.aspx.vb" Inherits="WhileLearning.WebForm1" 
    title="HandlingServerControlEvents" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
    <script language="VB" runat="server">
       Sub SubmitBtn_Click(Sender As Object, E As EventArgs)
           Message.Text = "Hi " & HttpUtility.HtmlEncode(Name.Text) & ", you selected: " & Category.SelectedItem.Text
       End Sub
   </script>
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
   <div>
   <center>
       <form id="Form1" action="HandlingServerControlEvents.aspx" method="post" runat="server">
           <asp:adrotator ID="Adrotator1" AdvertisementFile="ads.xml" BorderColor="black" BorderWidth="1" runat="server"/>
           <h3> Name: <asp:textbox id="Name" runat="server"/>
           Category:  <asp:dropdownlist id="Category" runat="server">
                         <asp:listitem >psychology</asp:listitem>
                         <asp:listitem >business</asp:listitem>
                         <asp:listitem >popular_comp</asp:listitem>
                      </asp:dropdownlist>
           </h3>
           <asp:button ID="Button1" text="Lookup" OnClick="SubmitBtn_Click" runat="server"/>
           <br />
           <asp:label id="Message" runat="server"/>
       </form>
       </center>
   </div>
</asp:Content>

[Resolved]