Ciao! I read the FAQ about this problem, i have unloked all permission of the do.php in ftp, but the problem remain. When i go to unsubscription process by the link in the e-mail newsletter i have a internal server error page.
I have installing WordPress 3.4.2 and newsletter 2.5.2.7 plugin
Usually this is die to file permission of the file “do.php” in the plugin folder. Try to ask your provider why that file cannot be called directly (it should).