Welp, I got my answer:
"I understand you’re encountering an error when attempting to log into your account. The error code you’ve received is a result of this account only having Beta Access, as no serial key was applied before the Free-to-play update. Having said that, there are a few ways to fix the issue. The simplest method to get into the game is to create a brand new Free-to-play account by registering a new account on our website here: https://account.arena.net/register
Once your account is created, you can submit a ticket requesting for the E-mail to be changed or swapped as you desire. Please be sure to provide information regarding both accounts if you decide to have your email swapped.
Alternatively, you may purchase a serial key and apply it to your Beta Account via the Account Management page. Once the key has been applied, you’ll be able to log into the game as normal. Please note there are no additional rewards for an account having participated in the Beta.
I hope this information helps! Please let us know if you have any other questions or concerns.