i hope you solved your problem. I am a nwebie here so i am afraid i can´t help, but since you are using class ps_payment maybe you can help.
I am building my first Virtuemart. Paypal is working fine but i can´t set credit card payment with ps_authorize. BUT i get no error when i process credit card payments setting class to ps_payment.
Is this save? can you tell me more about using this option? i cant find any tips in this forum, maybe i should try harder...