From my experience basically that means that you have google checkout as
your only means of payment and the user doesn't click on the google
checkout button so it proceeds to the other step when hes supposed to be
able to choose credit card processing, paypal or some other payment method.
The problem is if you have none of those other payment methods you'll
get that message. My solution was to hack up the store so that instead
of checkout button it will only show google checkout and the user has to
click it.
I hope that helps.
--
Igor Hernandez
Escape Communications
http://www.escapetel.com