During 2016 we've done a complete rebuild of Wordalist, from the ground up. As a result all users registered before 2016-05-22 need to change their passwords.
To do this - just go to the lost password page and enter your email. You'll get a link to your email address within a minute, just follow the instructions to choose a new password.
Why changing passwords?
The platform update means that we're changing the way we're encrypting user passwords. Without getting too techy - the previous encryption was well secure but could not be used in the new platform and updating existing passwords was not an option, as the encryption made it impossible for us to decode and re-encode them.