I've had reports over the last few months that people have been experiencing problems with the visual confirmation step during registration.
I have tested created users and do not see this problem. In only one case was I able to see it. It is most likely a session handling problem, so if you are getting this error and you KNOW you're entering the confirmation code correctly, then try REFRESHING the page and getting a new code. In my own testing, this seemed to work. If you are still having trouble creating an account, you can email me beck -at- iowclan -dot- com, and I will attempt to help you.
I apologize for the inconvenience.