Hi, got the same error today. Almost gave me a small heart attack … I’m just using Steam on one computer and never logged in anywhere else but I just published a Youtube video about Flight Simulator yesterday, so immediately I thought my account might have been hacked. But I logged out of the XL account, logged back in and restarted the sim. Then it let me proceed again. But I did have to turn on the online access in the Data Options menu.
All in all, probably just a glitch in the sign-in process (I hope!).