I, along with a number of others on the All-Stars forum have been having this issue (or a variation). When I click on the "PSN BETA" link, I'm told that I don't have the appropriate permissions. Dunno why though.
I have the same issue of being about to play the Betas, but getting access denied on the website. I called the tech support line and they took quite a while and gave me this non-resolution. If you can believe it, they told me I had to write a Snail Mail letter, yes, snail mail, to:
SCEA PO Box 5888 San Mateo CA 94402-0888
The Tech had no idea who to attention the letter to, but suggested "Beta Website problem"
Now this is SO dumb! Why can't they fix this without me writing a letter... even an e-mail is a bit much, but a snail mail letter to a PO Box!!!! Come on Sony!