I try to send an e-mail using a template in Kentico. The mail is sent correctly but the macros in the template are not resolved. resolver.ResolveMacros(template.TemplateText) returns "".

This is the method:

private void SendEmailUsingTemplate(string recipientEmail, string[,] replacements, string eventName)
        {
            // Set resolver
            ContextResolver resolver = CMSContext.CurrentResolver;
            resolver.SourceParameters = replacements;

            // Get the email template
            var template = EmailTemplateProvider.GetEmailTemplate("MembershipTest-RegistrationConfirmation", _applicationSettings.KenticoSiteName);

            if (template != null)
            {
                // Email message
                var emailMessage = new EmailMessage
                {
                    EmailFormat = EmailFormatEnum.Default,
                    Recipients = recipientEmail,
                    From = EmailHelper.GetSender(template, SettingsKeyProvider.GetStringValue(CMSContext.CurrentSiteName + ".CMSNoreplyEmailAddress")),
                    CcRecipients = template.TemplateCc,
                    BccRecipients = template.TemplateBcc,
                    Subject = resolver.ResolveMacros(template.TemplateSubject),
                    PlainTextBody = resolver.ResolveMacros(template.TemplatePlainText)
                };

                // Enable macro encoding for body
                resolver.EncodeResolvedValues = true;

                emailMessage.Body = resolver.ResolveMacros(template.TemplateText);

                // Disable macro encoding for plaintext body and subject
                resolver.EncodeResolvedValues = false;

                try
                {
                    MetaFileInfoProvider.ResolveMetaFileImages(emailMessage, template.TemplateID, EmailObjectType.EMAILTEMPLATE, MetaFileInfoProvider.OBJECT_CATEGORY_TEMPLATE);
                    // Send the e-mail immediately
                    EmailSender.SendEmail(CMSContext.CurrentSiteName, emailMessage, true);
                }
                catch (Exception ex)
                {
                    var eventLogProvider = new EventLogProvider();
                    eventLogProvider.LogEvent("E", eventName, ex);

                    throw;
                }
            }
        }

And this is the method call:

string[,] replacements = new string[1, 2];
replacements[0, 0] = "username";
replacements[0, 1] = username;

SendEmailUsingTemplate("eapeldoorn@snelstart.nl", replacements, "Test - Sending Emails");

Mailtemplate only contains the following:
{%username%}

Does someone have any idea?