try deleting the following files:
then create a new page, and add universal email to it. the settings used don't matter, we just want to regenerate those files, you can delete the page after UE is added, then upload the newer versions of thewebassist/email/mail_php.php and webassist/email/mailformatting_php.php
i'm thinking that since you had UE 4 installed previously, you have old copies of the files in the site.
also,, for troubleshooting, add the following code on the success page near the </body> tag:
<?php @session_start(); var_dump($_SESSION); ?>
this will write the session contents including the email status to the page