This can happen if you use your insecure domain or an http protocol in the URL for your donation form. By doing this, the system is forced to redirect the user to the secure domain on https, which will potentially drop the email message from the session variable. To find the correct link, use the WYSIWYG Editor.
  1. Highlight some text and click the hyperlink icon (chain link)
  2. Click Browse Links
  3. Click Donation Form
  4. Find and click your donation form
  5. Click Select
  6. Either click Insert to create the hyperlink, or copy the URL beside Link URL and add it where desired