Error: This webpage has a redirect loop

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C#

C#4.0

ERROR:This webpage has a redirect loop
The webpage at http://localhost:12205/kreu.aspx?ReturnUrl=%2findex.aspx has resulted in too many redirects. Clearing your cookies for this site or allowing third-party cookies may fix the problem. If not, it is possibly a server configuration issue and not a problem with your computer.

I have created a login system like this but when i run it gives the error

protected void btn_login_Click(object sender, EventArgs e)
        {


            string strCon = ConfigurationManager.ConnectionStrings["ConnectionStringusers"].ConnectionString;

        string strSelect = "SELECT COUNT(*) FROM [Users] WHERE UserName = @Username AND Password = @Password";

 

        SqlConnection con = new SqlConnection(strCon);

        SqlCommand cmd = new SqlCommand();

        cmd.Connection = con;

        cmd.CommandType = CommandType.Text;

        cmd.CommandText = strSelect;

        SqlParameter username = new SqlParameter("@Username", SqlDbType.VarChar, 50);
     username.Value = username_id.Value.Trim().ToString();

        cmd.Parameters.Add(username);


        SqlParameter password = new SqlParameter("@Password", SqlDbType.VarChar, 50);

        password.Value = password_id.Value.Trim().ToString();

        cmd.Parameters.Add(password);

        con.Open();

        int result = (Int32)cmd.ExecuteScalar();

        con.Close();

 

        if (result >= 1)

        {

            Response.Redirect("kreu.aspx");

            Session["username"] = username_id.Value;
            
        }

        else

           Response.Write(@"<script language='javascript'>alert('Invalid username or password!') </script>");

 

    } 
     

        }
}