Recently over 180,000 spambots were deleted from the system. In and amongst those, a number of regular users were also (accidentally) deleted.
If your forum name starts with A or with Ba - Bh, your account was accidentally wiped out and you need to sign up again. I imagine you could use the same forum name.
It's possible, but highly unlikely, that other legitimate accounts were also scrubbed. If you can't log in, please re-register.
Apologies for the inconvenience.