Thank you for reaching out to us on this! After reviewing the contents of your email, the reason that you received the 400 error was because the email contained characters that are not in the ISO-8859-1 character set that Constant Contact uses for our email campaigns.
In this case, the culprit was two instances of the character '€'. The best way to resolve this is to take characters that are not part of the character set and encode that as HTML entities so that they can be still be sent, and will be rendered on the client. For this specific character, the corresponding HTML entity is '€'.
As a side note, I removed the attachment from your post, as it contained some sensitive information that it would be better not to have available on a public forum such as this.