You have not activated your new account within 7 days of registering.
You have not had any activity in the forum for the past 180 days.
That being said if your post count exceeds 300 posts, I will not try not to delete your account. (this condition was added on 8/12/09)
So if you find that all of a sudden you can't login, odds are that your account was purged. Try creating a new forum account and that should take care of things in most cases. Purging of inactive accounts is done to keep the database optimised and reduce screen load times. If you are an infrequent user, then you may have to reregister again.
For those of you who are Site Supporters
Account will be deleted regardless of whether you are a Site Supporter or not. Please understand that the database purges usernames regardless of your forum status. Don't take it personally, that's just the way the software works. If you find your account was deleted simply create a new forum account and send me a note telling me that you would like to have your Site Supporter status added to your new account. I'll be happy to do that for you.
-- Frank --