Simplenews send empty mail

I try to send an email bij using Simplenews, Sinplenews_template and mimemail. I got the message:

warning: Missing argument 3 for _simplenews_template_theme_simplenews_newsletter_body() in /www.domain/public_html/sites/all/modules/simplenews_template/simplenews_template.module on line 370.
recoverable fatal error: Object of class stdClass could not be converted to string in /www.domain/public_html/sites/all/modules/simplenews/simplenews.module on line 1557.
recoverable fatal error: Object of class stdClass could not be converted to string in /www.domain/public_html/sites/all/modules/simplenews/simplenews.module on line 1557.

The mail arrived but there is no text in it, only:

Object -- Unsubscribe from this newsletter: http://www.domain/newsletter/confirm/remove/ - - - This is a test version of the newsletter. - - -

Is this a bug?