When you register your business and create your user account, you will receive an email to the address registered asking you to activate your user account by clicking a unique link in the email. If you do not do this, you will be unable to login with your new credentials, although your business listing may still appear in the Shop Green directory.
To solve: Please check your inbox and spam folders for emails from WordPress and/or Thurston Green Business asking you to activate your account, and click on the link inside the email.