You seem to be trying to a newsletter email. However, these emails are site objects which are assigned to a particular site. You seem to be triggering the action or whole process in context of a different site.
You can copy newsletters and emails to site which is running MA process. Or you can wrap action in CMSActionContext and set CurrentSite property for the context, but for this I can not guarantee behaviour of API and contextual properties as this was not thoroughly tested...