We have made a fix to the 'user_payment.php' file after release 3.2 has been issued.
 
Description.
There was a bug in the user_payment.php.file. It doesn't first setup the payment_id parameter before using it on line 49.
 
Solution.
Please, download an updated version of the 'user_payment.php' file from here:
http://www.viart.com/downloads/user_payment-3.2.zip
Then extract the fixed file into the root folder of your shop replacing an existing one.
Don't forget to make a backup copy of the current file in case something goes wrong.