Cause: Make sure you're using the password for the website and not your IRC Nickname. They're not necessarily the same passwords.
Cause: Make sure you're using a supported Web browser.
Answer: IRC nicknames must be unique, less than 30 characters in length, use supported characters (A-Z, a-z, 0-9, |, {}, [], (), _ ) and contain no spaces or other unsupported characters (!, @, #, $, %, &, *)
Cause: Accounts that are created but then don't either get drilled or perform rescues, are soft-deleted for inactivity after 30 days to keep the roster cleaner. Once you have a rescue to your name, or are drilled, the account is permanent. If you still can't access it then, contact the helpdesk.