Problem with the Code Handling User Registration and Send Activation Link

 using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;
using System.Net;
using System.Net.Mail;
using System.Data;

public partial class AdminAddCandidate : System.Web.UI.Page
{
    DBClass db1 = new DBClass();


    protected void Page_Load(object sender, EventArgs e)
    {

    }

    protected void BtnRegisterCand_Click1(object sender, EventArgs e)
    {
        int userId = 0;
        db1.sqlcmd = new SqlCommand("USP_Register_Candidate");

        using (SqlDataAdapter sda = new SqlDataAdapter())
        {
            db1.sqlcmd.CommandType = CommandType.StoredProcedure;
            db1.sqlcmd.Parameters.AddWithValue("@UserName", TxtBxCandUsername.Text.Trim());
            db1.sqlcmd.Parameters.AddWithValue("@CNIC", TxtBxCandCNIC.Text.Trim());
            db1.sqlcmd.Parameters.AddWithValue("@Email", TxtBxCandEmail.Text.Trim());
            db1.sqlcmd.Parameters.AddWithValue("@RecoveryEmail", TxtBxCandRecoveryEmail.Text.Trim());
            db1.sqlcmd.Connection = db1.sqlcon;
            db1.sqlcon.Open();
            userId = Convert.ToInt32(db1.sqlcmd.ExecuteScalar());
            db1.sqlcon.Close();
        }

        string message = string.Empty;
        switch (userId)
        {
            case -1:
                message = "Username already exists.\\nPlease choose a different username.";
                break;
            case -2:
                message = "Supplied email address has already been used.";
                break;
            case -3:
                message = "Supplied CNIC has already been used.";
                break;
            default:
                message = "Registration successful.\\nUser Id: " + userId.ToString();
                SendActivationEmail(userId);
                break;
        }
        ClientScript.RegisterStartupScript(GetType(), "alert", "alert('" + message + "');", true);
    }

    private void SendActivationEmail(int userId)
    {
        string activationCode = Guid.NewGuid().ToString();
        db1.sqlcmd = new SqlCommand("USP_CandidateActivation");
        using (SqlDataAdapter sda = new SqlDataAdapter())
        {
            db1.sqlcmd.CommandType = CommandType.StoredProcedure;
            db1.sqlcmd.Parameters.AddWithValue("@UserId", userId);
            db1.sqlcmd.Parameters.AddWithValue("@ActivationCode", activationCode);
            db1.sqlcmd.Connection = db1.sqlcon;
            db1.sqlcon.Open();
            db1.sqlcmd.ExecuteNonQuery();
            db1.sqlcon.Close();
        }
        using (MailMessage mm = new MailMessage("sender@gmail.com", TxtBxCandEmail.Text))
        {
            mm.Subject = "Account Activation";
            string body = "Hello " + TxtBxCandUsername.Text.Trim() + ",";
            body += "<br /><br />Please click the following link to activate your account";
            body += "<br /><a href = '" + Request.Url.AbsoluteUri.Replace("AdminAddCandidate.aspx", "CandidateAccountActivation.aspx?ActivationCode=" + activationCode) + "'>Click here to activate your account.</a>";
            body += "<br /><br />Thanks <br /> Electoral Information System";
            mm.Body = body;
            mm.IsBodyHtml = true;
            SmtpClient smtp = new SmtpClient();
            smtp.Host = "smtp.gmail.com";
            smtp.EnableSsl = true;
            NetworkCredential NetworkCred = new NetworkCredential("someEmail@gmail.com", "somePassword");
            smtp.UseDefaultCredentials = true;
            smtp.Credentials = NetworkCred;
            smtp.Port = 587;
            smtp.Send(mm); 
        }
    }
}

CREATE PROC USP_CandidateActivation
@UserId INT, @ActivationCode UNIQUEIDENTIFIER
AS
BEGIN
INSERT INTO CandidateActivation (CandID,ActivationCode) VALUES(@UserId, @ActivationCode)
END

CREATE PROC USP_Register_Candidate
@UserName VARCHAR(30),@CNIC VARCHAR(13), @Email VARCHAR(50),@RecoveryEmail VARCHAR(Max)
AS
BEGIN
      SET NOCOUNT ON; 
      IF EXISTS(SELECT CandUserName FROM Candidates WHERE CandUserName = @UserName)
      BEGIN
            SELECT -1 -- User Name exists.
      END
      ELSE IF EXISTS(SELECT CandEmail FROM Candidates WHERE CandEmail = @Email)
      BEGIN
	  SELECT -2 -- Email exists.
	  END
	  ELSE IF EXISTS (SELECT CandCNIC FROM Candidates WHERE CandCNIC = @Email)
	  BEGIN
	  SELECT -3 -- CNIC exists
	  END
	  ElSE
	  BEGIN
INSERT INTO Candidates (CandUserName,CandEmail,CandRecoveryEmail,CreatedDate,CandCNIC) VALUES(@UserName,@Email,@RecoveryEmail,GETDATE(),@CNIC) SELECT @@IDENTITY

            SELECT SCOPE_IDENTITY() -- CandID                 
     END
END