Still getting An asynchronous module or handler completed while an asynchronous operation was still pending

Question

I know this question has already been asked (SendMailAsync : An asynchronous module or handler completed while an asynchronous operation was still pending ) but I'm obviously still doing something wrong as I'm still getting the following error:

An asynchronous module or handler completed while an asynchronous operation was still pending.

This is my controller's code:

[HttpPost]
[AllowAnonymous]
[ValidateAntiForgeryToken]
public async Task<ActionResult> ForgotPassword(ForgotPasswordViewModel model)
{
    if (ModelState.IsValid)
    {
        var user = await UserManager.FindByNameAsync(model.Email);

        if (user == null || !(await UserManager.IsEmailConfirmedAsync(user.Id)))
        {
            bool isApproved = IsOrganizationForMemberApproved(user);

            if (!isApproved)
            {
                ModelState.AddModelError("", "Your organization has not been approved.");
                return View(model);
            }

            // Don't reveal that the user does not exist or is not confirmed
            return View("ForgotPasswordConfirmation");
        }

        await CustomEmailService.SendPasswordReset(this, UserManager, Request, user);

        return RedirectToAction("ForgotPasswordConfirmation", "Account");
    }

    // If we got this far, something failed, redisplay form
    return View(model);
}

And this is my email helper function:

    public static async Task SendPasswordReset(Controller controller,
        ApplicationUserManager userManager,
        HttpRequestBase request,
        ApplicationUser user)
    {
        string code = await userManager.GeneratePasswordResetTokenAsync(user.Id);
        var callbackUrl = controller.Url.Action("ResetPassword", "Account", 
        new { userId = user.Id, code = code }, protocol: request.Url.Scheme);

        var message = LoadPasswordResetMessage(callbackUrl);

        using (EmailManager emailManager = new EmailManager())
        {
            await emailManager.SendEmailAsync(user.Email,
                user.UserName, "Reset Password", message);
        }
    }

and finally the function responsible for sending the email:

public async Task SendEmailAsync(string toEmailAddress,
       toDisplayName, string subject, string htmlContent)
{
    //... read settings
    var message = new MailMessage();

    message.To.Add(new MailAddress(toEmailAddress, toDisplayName));
    message.From = new MailAddress(fromEmailAddress, fromDisplayName);
    message.Subject = subject;
    message.Body = htmlContent;
    message.IsBodyHtml = true;

    using (var smtp = new SmtpClient())
    {
        var credential = new NetworkCredential
        {
          UserName = smtpUserName,
          Password = smtpPassword
        };
        smtp.Credentials = credential;
        smtp.Host = smtpHost;
        smtp.Port = Convert.ToInt32(smtpPort);
        smtp.EnableSsl = Convert.ToBoolean(enableSsl);
        await smtp.SendMailAsync(message);
    }
}

What am I missing? Any help would be greatly appreciated.

Thanks.