[opencms-dev] Alkacon Newsletter 1.0.1 module configuration issue

[Sandrine Prousteau]

Hi
I'm trying to use the Alkacon Newsletter module (version 1.0.1). I'm on
OpenCms 7.0.5. 
I followed the tutorial on the pdf, but when I try to send a newsletter
to a mailing list (wich have a user associated), I click Ok when the
popup say "Are you sure you want to send the selected newsletter?", and
then nothing comes, the line of the newsletter appears in red and the
title of the link is "Newsletter can not be sent". WHY?
I've installed the Alkacon formgenerator too, and it works well, I can
receive contact form data on my mail adress. 
Could you help me to find the problem?