Wraps user account confirmation email with theme including an error message

I use Echo with Simplenews, HTML Mail and Mail system to send HTML mails to customers... that part works fine.
When a new user creates an account, an email is sent with the "waiting on approval" message... works fine
But when the administrator confirms the new account, he receives a themed email (with the screen theme, not the email theme) contaigning the following code and an error message:
"http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd">

xmlns:content="http://purl.org/rss/1.0/modules/content/"
xmlns:dc="http://purl.org/dc/terms/"
xmlns:foaf="http://xmlns.com/foaf/0.1/"
xmlns:og="http://ogp.me/ns#"
xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
xmlns:sioc="http://rdfs.org/sioc/ns#"
xmlns:sioct="http://rdfs.org/sioc/types#"
xmlns:skos="http://www.w3.org/2004/02/skos/core#"
xmlns:xsd="http://www.w3.org/2001/XMLSchema#">

When I deactivate Echo module, everything works fine except nothing is themed anymore