I'm having the same issue - after an order goes all the way through and I hit the last step <confirm order> and press that I get this error..
Fatal error: Cannot redeclare do_magic_quotes_gpc() (previously declared in /home/empirest/public_html/includes/functions/compatibility.php:18) in /home/empirest/public_html/includes/functions/compatibility.php on line 30
any idea's on what to look for and change.