When I try to add an answer to my Careers profile, it says that I don't have any, but I have answered some questions on Stack Overflow.
How can I solve this?
Your account Id was not set on Careers. It looks like this happened because you used a different open id to sign up for careers than you used when you signed up for the other sites which would cause this to happen.
I have updated it for you. Try again and let us know if you can see your stuff now.