Trados Enterprise / Live: "Error activating user in the account." when opening an email invitation link

When opening an invitation link from Trados Enterprise / Live, either from an invitation email or a manually provided link, the following message appears:

 

Log out and back in with the correct email address

 

1. Click the Logout button to log out of the current RWS ID.
    
2. If you already have an RWS ID associated with the correct email address then sign in with these credentials:
   
   
   
   If not, then click the Sign Up tab and complete the form to create a new RWS ID for your email address:
   
   

NOTE: In some cases, due to browser caching issues, the activation error may recur. If it does then clear the cache for Trados Enterprise / Live, and then close and re-open your browser. Then open the invitation link again.

You are logged into Trados Enterprise / Live as a different user to the one that the invitation is meant for.