Not sure if this would help, but you could reset your DNS cache if the above suggestions (logging out, clearing cache and cookies, etc) don't work.
To reset/purge your DNS cache, open a command prompt, and type:
ipconfig/ flushdns
You can also try renewing your IP address by typing the following into the command prompt (if flushing your dns doesn't work):
ipconfig/ renew
Then try logging into chat again.