If you have already registered but CANNOT log-in, the reason behind this is that YOU HAVE NOT ACTIVATED your account yet... try opening your e-mail ( the one you registered with) and look for the NPC AG message... then you have to click THAT link to be able to log-in and activiate your account. Once you have done that, then you can now log-in and log-out normally.
The other reason is that a user may have been banned by one of the moderators or admin... but so far, no one has been banned or removed. . .behave naman lahat eh.. he he he
