I've also had a lapsed Acorn account and added AcornTV via Roku. When I opened AcornTV I chose 'skip' rather than select a payment option (don't ask me why -- I'm not even sure I know).
I selected a show and was asked again for a payment option which I selected (and verified that I am now billed directly from my ROKU account). My lapsed account on Acorn is still inactive. I got the same error everyone else has reported and blocked from viewing.
I tried similar steps before I checked here including rebooting ROKU.
Is it possible that if the ROKU account email is different from the Acorn website account it is triggering this error?