You have to manually add a certificate exemption to your browser. But I wouldn't bother. Their system seems to be messed up. It either allows you to do one HIT and then tells you there's no more you can do because you have done them before or it tells you that you scored too low. I got the former reason which I found strange because I've only done a single Redwood HIT before, and that was in September. They're off for the weekend, so you could drop them a message via Mturk and then wait for a response on Monday.