So, there have been bunches of problems people have had with creating a new user account;
Either the activation email gets lost in the ether (or their spam folders) or occasionally, the activation link provided just doesn’t work.
I’m looking into it, but in the meantime, send me an email directly, and I’ll manually add you.
I’ve actually been working on a baseline single signon for the suite of athas.org sites, and I’ll be looking to fit that into Arena. Hopefully, that’ll end up working out better. Kinks and stuff to work through though.