The current Magento module (1.0.0) does not work properly on Magento 1.4.x Stable.
Please check the technical newsfeed for updates regarding a compatible version of our payment module.
***UPDATE***
The module 2.0.0 does offer support for 1.4.0.x but not yet for 1.4.1.x, there are 2 issues:
1) The "config.xml" file is missing some info required by 1.4.1.x
2) The "fee per paymentmethod" does not show up on order printouts (admin orders/invoices/refunds)