I’ve recently had to upgrade the security on this site, adding a Captcha feature for the creation of user accounts, posting comments and such. Unfortunately, in doing so, many of the existing user accounts got deleted. (I’m still not quite sure how that happened.) So you may need to create a new account if yours was one of the ones affected.
I’m really sorry about this, but I’ve checked into what went wrong, and I’m confident that it won’t happen again. In the meantime, please accept my apology for any inconvenience caused.