This appears to be an issue with the licencing disclaimer stuff. I had the same problem and sought assistance, despite having a valid login.If you open Windows Live from your windows start menu (not from in Flight), you can log in and you will likely be told that the terms of service will need updating since your last login (if you already had an account).
Accept the updated licence agreement for temrs of service (for Live, not Flight) and the problem goes away, allowing you to open flight normally.If you do not accept the licence agreement update, you see the request to enter a product key from within Flight itself. It has to be done from outside of Flight by opening Live from your programs menu directly.
Flight gets itself all confused and prompts for the key!all the bestJane W (PCPilot). This is the official 'workaround' from the MS Devs!!*****************************************************************************************Hi everyone! We've been hearing that people are getting asked for a product key when they try to log into LIVE and use Flight.Here's a workaround -- if you run across other people having this problem, please pass it on. Thanks!:-)Because Microsoft Flight is Free-to-Play when you sign-into LIVE for the first time through Flight a product key should be auto assigned to you.