A great new feature in Joomla 1.5.12 that allows you to send email over SSL SMTP breaks compatibility with our extensions (If you want to use that feature).
We are aware of the issue and will release new versions that can take advantage of this new feature as soon as we can. For the time being please use the other available mail options that have been available before (PHP Mail, SMTP, SMTP With Auth and Sendmail). The new SMTP over SSL feature will will incorporate for the next versions of our extensions.
More reading: PHPMailer version used in 1.5 does not allow secure connection to SMTP servers
UPDATE 02/Jul/09 6:47pm GMT: The additional code has now been written to support GMail/SSL/TLS connections for bfForms email sending – if you need this update before the official release please email me direct