I have tried 2 different OpenID accounts to try to register and in each case I get an error and cannot register
I have cut and pasted the links suggested by both my openID accounts into the URL box on the registration page and nothing works
If you have a dot in your user name, such as first.last.myopenid.com, you can't use the normal link to register; you will need to click the link to manually enter your ID, then enter it manually at the openid site.
I have this problem, and found the answer somewhere on the stackoverflow site.
For more information, see this discussion: stackoverflow openID problem