Ubuntu 10.04 64 bit
tried chrome and firefox
Used OpenID cannot log in to chat.
UPDATE
the thing that worked for me was
There is also a secondary option; log in to your preferred Stack Exchange site, and edit the URL (usually at the top of your browser) to http://{your stackexchange site.com}/users/chat-stackexchange-login, for example: https://gaming.stackexchange.com/users/chat-stackexchange-login.
This line should be placed ABOVE the line on contacting meta.stackoverflow.com