[TYPO3-commerce] tx_commerce payment "debit"

[Attila Sirman]

Hello list,

this may be a repeated question, but since I found little support on the 
web, I feel urged to ask again:

I am running a Typo3 (4.3.3) installation with tx_commerce (0.9.9). 
Everything works fine, except:

The payment procedure with "debit" chosen ends up after filling in the 
bank details (refuses next step). I implemented the method by adding the 
global config in /ext/commerce/ext_localconf.php. The payment article 
appears in BE & FE (as payment method). The included class is obviously 
loaded since the defined locallang values and form fields appear. I have 
no clue where the script stops.

Any suggestions?
Thanks in advance for help.
Attila