TOPIC: Blank screen with Authorize.net

I started to use DT Register Joomla 1.5 with Authorize.net. The single user registration works just fine. However the group registration goes to a blank screen when Submit is clicked for processing. Paypal seems to work fine in both modes. I searched for issues with Blank screen and Authorize...and tried them (taking out custom fields, CURL being on etc)...nothing worked.