The Wizard generates this message if it cannot find the TARGET_EMAIL setting in your formmail.php.
The most likely cause of this is that you may have deleted one of these lines:
If that's the cause, you can try putting them back before upgrading, but it's probably better to just download the new version and configure it manually.
/* CONFIGURATION (do not alter this line in any way!!!) */
/* END OF CONFIGURATION (do not alter this line in any way!!!) */
If that's not the cause, please email your formmail.php as an attachment to supportstaff AT tectite DOT com.