This is related to missing permissions on your forums account. Please try these troubleshooting steps in order:

🛠 Make sure you are logged in to the Age of Empires forums, and then re-try any provided links to the closed beta section you are trying to reach.

🛠 Check that you are using the same Microsoft account to sign into the forums as your Age of Empires Insider account. You can confirm this by comparing the gamertag on your Age Insider profile with your username on the Age of Empires forums. They should be the same. If they are not, then you have created two (2) separate accounts and will need to log-out, and create a new Age of Empires forums account with the same Microsoft account as you used to sign-in to your Age Insider Profile.

🛠 Fully log-out of the forums from all devices. After you have logged out, delete your browser’s cache and cookies, and then sign in to the forums again. Generally speaking, changes in permissions on the forums occur during next sign-in. 

If the steps above do not resolve your issue, please reach out to AOEInsiderSupport@microsoft.com for assistance. We will need your gamertag and the URL of the forums page you are trying to access; a screenshot of any error messages can also help diagnose any potential alternative problems.