Clicking the invitation link gives me the following error message:
Welcome to Stack Overflow Careers!
Thanks for your interest in creating a profile on Stack Overflow Careers.
We can’t seem to find that invitation. It’s possible that it has been used already or has expired.
This occurred after I got the "email address is already in use" error. And then logged out/in with my openid account (as suggested). I tried logging back in to careers with the original username/pass I used. However it won't let me now that I have used an openid associated with the email I used to create the account. So my invitation is stuck on an account sitting in limbo.