A page can have only one server-side Form tag.
asp.net, forms, master-pages
Solution
Master pages should not contain `form` tags in general because they are meant to be used only as the base layout of your content page. Remove the `form` tag from the Master page and the error will go away.
If you want to define a common "Login" section for all your pages (this appears to be your intent), you can instead create a `UserControl` to do this. You would then define a section inside your Master page to contain this user control making sure that the ContentPlaceHolder of the Login UserControl always ends up enclosed inside the content page's `form`. That way, when you submit the form, the `btnlogin_Click1` click event is triggered.
In conclusion: re-arrange your page in a way that you have one `form` tag per page, since ASP.NET does not allow having more than one and try to define your form's inside the content pages and not the Master page.
Problem
Masterpage.aspx ``` <html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server"> <title></title> <asp:ContentPlaceHolder ID="head" runat="server"> </asp:ContentPlaceHolder> <script src='http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js'> </script> <script src="Chrome.js" type="text/javascript"></script> </head> <body> <form id="Master" runat="server"> <table style="width:987px; margin:auto; height: 86px;"> <tr style="background-color:#FFFFFF"> <td class="style2"> <img src="images/logo.jpg" alt="" width="235" height="73" /> </td> <td style="vertical-align:middle;"class="style1"> <div style="float:right; width:153px; height: 22px;"> <asp:TextBox ID="TextBox1" runat="server" Height="20px" style="margin-left: 0px" Width="140px"> </asp:TextBox> </div> <a href="">Forget Password?</a> </span></span> </td> <td class="style33"> <div style="float:right; width:157px; height: 20px; margin-right: 1px;"> <asp:TextBox ID="TextBox2" runat="server" Height="20px" style="margin-left: 0px; margin-top: Width="147px"></asp:TextBox> </div> <a href="Registration.aspx">New User Registration</a> </span> </td> <td class="style40"> <div style="height: 67px; width: 81px;">  <asp:Button ID="btnlogin" runat="server" style="color:White; background-color:#404040;font-family:Verdana;font-size:10pt; height: 29px; margin-top: 12px;" Text="Login" onclick="btnlogin_Click1" /></div> </td> </tr> </table> </td> </tr> <tr style="background-color:#207DA8"> <td class="style39"> </td> <td class="style39"> </td> </tr> <script type="text/javascript"> cssdropdown.startchrome("chromemenu") </script> </td> </tr> <img alt="" src="images/rgt.jpg" style="width: 471px; height: 247px" /> </td> </tr> <tr style="vertical-align=top;background-color=#D4D3D9"> <td style="height:1;"> </td> </tr> </tbody> </table> </tbody> </table> <asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server"> </asp:ContentPlaceHolder> </form> </body> </html> ``` RegisterPage.aspx ``` <%@ Page Language="C#" MasterPageFile="~/MasterPage.Master" AutoEventWireup="true" CodeBehind="Registration.aspx.cs" ValidateRequest="false" Inherits="Paragraphreader.Registration" %> <asp:Content ContentPlaceHolderID="ContentPlaceHolder1" runat="server"> <script src="jquery.validate.js" type="text/javascript"></script> <script src="jquery.validation.js" type="text/javascript"></script> <script> $("#Register").submit(function () { return $(this).validation(); alert("submitted"); }); </script> <script> function validate() { var a = 0, rdbtn = document.getElementsByName("gender"); for (i = 0; i < rdbtn.length; i++) { if (rdbtn.item(i).checked == false) { a++; } } if (a == rdbtn.length) { document.getElementById("RadioButtonList1").style.border = "2px solid red"; return false; } else { document.getElementById("RadioButtonList1").style.border = ""; return true; } } </script> <link href="Career.css" rel="stylesheet" type="text/css" /> <link href="Chrome.css" rel="stylesheet" type="text/css" /> <link href="Styles.css" rel="stylesheet" type="text/css" /> <form id="Register" runat="server">//A page can have only one form tag <asp:ScriptManager ID="ScriptManager1" runat="server"> </asp:ScriptManager> <asp:UpdatePanel ID="FormUpdatePanel" runat="server"> <ContentTemplate> ``` I am getting error(A page can have only one server side cof while compiling RegisterPage.aspx.In the master page i have a form tag and server side code In the Register page i have a form tag and server side code.how to avoid this error