Hi,
i’m trying your plugin ( nice work, compliment! 
) but i have a little problem:
when i try to subscribe to mailing-list (page with form: http://www.festadelpesce.org/sito/newsletter/) i receive an internal server error message (http://www.festadelpesce.org/sito/wp-content/plugins/newsletter/subscription/page.php?nm=error&nk=1-55f4ea376f)…
Server permission of directories and files are 755.
Can u help me please?
Thanks,
bye!