Updated to v2.3, Using WP 3.5.1
Clicking on the preview button for the newsletter gives this error:
Fatal error: Call to a member function replace_subject() on a non-object in /home/user/public_html/wp-content/plugins/wysija-newsletters/helpers/mailer.php on line 630
Also, now it doesn't work the send preview either. It freezes on the "Sending preview..." popup forever.
Downgraded to 2.3.3 and both things works again.