Hi Fallen,
go to
www.enatural.ro and buy something using username "fallen" and pass "1234".
When the order should be complete I get that message.
This site is in another language, not in English, but in Romanian.
In romanian you'll get the message "Error: Va rugam selectati o alta modalitate de expediere.", translated phrase from english.
I remember having a problem like this with artio 1.4.1 and the VirtueMart plugin (not yours).
Your VirtueMart plugin worked very well with JoomSef 1.5.1., but the new one made for 2.1.0 not so well.
Thank you,
Marius