i m facing below error 

Invalid postback or callback argument.  Event validation is enabled using <pages enableEventValidation="true"/> in configuration or <%@ Page EnableEventValidation="true" %> in a page.  For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them.  If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation.

<%@Page enableEventValidation="f" Title="" Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="adminlogin.aspx.cs" Inherits="administrater_adminlogin" %>

<asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" Runat="Server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" Runat="Server">

<div style="height: 387px; width: 832px; margin-left: 3px; background-image: url('../IMAGES/admin_login.gif');" 
        align="center">
<form id="form1">
<br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br />

    <div >
       <div style="width: 402px" >&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;<asp:Label ID="Label1" runat="server" 
               Text="Admin id" Font-Bold="True" ForeColor="#003399"></asp:Label>&nbsp;&nbsp;&nbsp;&nbsp;
           <asp:TextBox ID="uid" runat="server" Width="209px" BorderColor="#003366" 
               BorderStyle="Solid" BorderWidth="1px" ></asp:TextBox>
       </div>
    <div style="width: 400px" >&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;<asp:Label ID="Label2" runat="server" 
            Text="Password" Font-Bold="True" ForeColor="#003399"></asp:Label>&nbsp; &nbsp;
        <asp:TextBox ID="upass" runat="server" Width="209px" TextMode="Password" 
            BorderColor="#003366" BorderStyle="Solid" BorderWidth="1px" 
            ></asp:TextBox>
       </div>
    <div  style="width: 

400px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
        <asp:Button ID="Button1" runat="server" Text="Login" BackColor="#003366" 
            BorderStyle="Solid" BorderWidth="1px" Font-Bold="True" ForeColor="White" 
            onclick="Button1_Click" />
        <asp:Button ID="Button2" runat="server" Text="Reset" BackColor="#003366" 
            BorderStyle="Solid" BorderWidth="1px" Font-Bold="True" ForeColor="White" 
            onclick="Button2_Click" />
        <asp:Button ID="Button3" runat="server" BackColor="#003366" BorderStyle="Solid" 
            BorderWidth="1px" Font-Bold="True" ForeColor="White" Text="Back" 
            onclick="Button3_Click" />
        <div 

>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
            <asp:Label ID="Label3" runat="server" 
                Text="user id or password is wrong" Visible="False" Font-Bold="True" 
                ForeColor="#CC0000" BackColor="White"></asp:Label></div>
       </div>
    </div>
    </form>
</div>


</asp:Content>