No overload for method 'Send' takes '5' arguments

please try with MailMessage object and smtp.Send will not take 5 argument.

protected void ImgBtnSubmit_Click(object sender, ImageClickEventArgs e)
    {
        try
        {

            string toadd = "info@abc.co.uk";
            var fromAddress = "info@abc.co.uk";

            var toAddress = toadd;
            const string fromPassword = "abc";
            string subject = "Contact";

            string bcc = "xyz@abc.co.uk";
            string body = "<table border=1><tr><td> Name </td><td>" + txtname.Text + "</td></tr>" +
                    "<tr><td> Telephone </td><td> " + txttel.Text + "</td></tr>" +
                    "<tr><td> Mobile </td><td> " + txtmobile.Text + "</td></tr>" +
                    "<tr><td> Email </td><td> " + txtemail.Text + "</td></tr>" +
                    "<tr><td> Query </td><td> " + txtquery.Text + "</td></tr></table>";

            var smtp = new System.Net.Mail.SmtpClient();
            {
                smtp.Host = "mail.abc.co.uk";
                smtp.Port = 25;
                smtp.EnableSsl = false;
                smtp.DeliveryMethod = System.Net.Mail.SmtpDeliveryMethod.Network;
                smtp.Credentials = new NetworkCredential(fromAddress, fromPassword);
                smtp.Timeout = 20000;
            }
            MailMessage msg = new MailMessage();
            msg.From = new MailAddress(fromAddress);
            msg.To.Add(new MailAddress(toAddress));
            msg.Bcc.Add(new MailAddress(bcc));
            msg.Subject = subject;
            msg.Body = body;
            msg.IsBodyHtml = true;

            smtp.Send(msg); 

            Response.Redirect("replycontact.aspx");

            txtname.Text = "";
            txttel.Text = "";
            txtmobile.Text = "";
            txtemail.Text = "";
            txtquery.Text = "";
        }
        catch (Exception) { }
    }

The answer is simple:

SmtpClient has exactly two Send methods. The first takes simply a MailMessage instance and the second takes exactly four string parameters.

Look here: SmtpClient.Send Method[^].

Being able to read is a good thing, use it every day!

Cheers!