While I am trying to get my API key, it is throwing me an error.
http://community.constantcontact.com/t5/Documentation/API-Keys/ba-p/25015. To replicate try to login as an any user and go to API key get your API Key- it throw an error then.
I did see this error yesterday but wasn't able to reproduce it again. I'll have our engineering team look into this and see if we can get this resolved. In the meantime, I would recommend clearing your cookies or trying a different browser.