If you’ve changed your username then I’d bet that’s what is confusing PsychoPy - when you login, PsychoPy sends a request to the Pavlovia server saying “give me the details for the user called…”, and the server replies. It looks like whatever the server is responding with, it’s not a set of user info, which is what causes the error. What is your new username, and what did you change it from? I can try sending the request manually to see how the server responds.
You may also find this useful:
as you can then get a more helpful error message in the app