Newline in constant error

Can someone clue me in what this error is talking about?

Here is the code:
if (reader.HasRows)
            {
                if (tbUserName.Text == reader["USERNAME"].ToString())
                {
                    if (tbPassword.Text == reader["PASSWORD"].ToString())
                    {
                        physicianNPI = reader["PHYSICIAN_NPI"].ToString();
                        Session.Add("physicianNPI, physicianNPI);--------------------------Error on this line
                        Response.Redirect("Portal.aspx");
                    }Start Free Trial