My mail System Running Fine on Local Machine But gives error on Net

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.NET3.5

C#

.NET

I am using .Net3.5 with C#,

This is my code

protected void btnSubmit_Click(object sender, EventArgs e)
        {
            try
            {
                string mailto = "xxxxxxx@gmail.com";
                MailMessage messagemail = new MailMessage();
                MailMessage mymessage = new MailMessage();
                mymessage.From = new MailAddress("yyyyyy@gmail.com");
                mymessage.To.Add(mailto);
                mymessage.IsBodyHtml = true;
                mymessage.Subject = "Queries";
                mymessage.Body = "Name:" + TxtName.Text + "\nEmail Id:" + TxtEmailId.Text + "\nAddress:" + TxtAdress.Text + "\nMobile No.:" + TxtMobile.Text + "\nQueries/Feedback:" + TxtQueries.Text + "";
                SmtpClient sc = new SmtpClient();
                System.Net.NetworkCredential mycred = new System.Net.NetworkCredential("yyyyyy@gmail.com", "********");
                sc.Host = "Smtp.gmail.com";
                sc.Port = 587;
                sc.EnableSsl = true;
                sc.UseDefaultCredentials = false;
                sc.ServicePoint.MaxIdleTime = 1;
                sc.Credentials = mycred;
                sc.Send(mymessage);
                mymessage.Dispose();
                ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "aa", "javascript:alert('Thanks For Contacting Us. We Will Get Back To You Soon')", true);
                TxtName.Text = "";
                TxtAdress.Text = "";
                TxtEmailId.Text = "";
                TxtMobile.Text = "";
                TxtQueries.Text = "";
            }
            catch (Exception ex)
            {
                ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "aa", "javascript:alert('"+ ex.Message +"')", true);
            }
        }

Its running Fine on local machine, but when I upload my web page it gives the following error

"The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required."

Although i used
sc.EnableSsl = true;

Please Help
Thanks
Faiz

[edit]Code block added - OriginalGriff[/edit]