I tried to log in from the home page with an account which already existed from a prior version of CB.

I got a message that the page I was trying to acces does not exist. Clicking on OK got me back to the home page and I was logged in fine.

(Safari + Mac - latest versions).

Try using the search feature before you post. If you did, you would see numerous posts, including many in an 11 page thread, about this already. This is a Joomla problem, not a CB problem. Remember to put the 'www' in front of the url.