I checked VPNbook out, was able to get to the register page when using the US servers, but on Canadian and Russian servers I just get the page that says they've banned me from registering an account/contact an administrator if it is an error.
Is this related to their banning of people who advertise adblock?
I understand where they're coming from, they have a right to defend their source of revenue but IMO antagonizing the adblock users is just shooting themselves in the foot. At this point, politely asking people to just whitelist their site would have worked better.
