A number of users have attempted to create user accounts and most likely came across some errors during the sign-up process. I have since fixed the problems and a back-log of e-mails were just now sent out. Some of the links in the older e-mails may not work. If so, simply visit YakyuDB as you normally do and use the login button in the top menu area.
If you are still having problems with your account, please drop me an e-mail at info at yakyudb.com.
My apologies for the inconvenience.