This exact same Error started to happen for me a Week Ago. Just happened Once. but Since yesterday i can’t get past the Login Screen. Before i even see my Warband the Error occurs, every Time i try to get into Character Selection. i REALLY hope this is one Blizz’s End and not because of my Pc. im Getting worried over here.
EDIT*
After my Comment got Split here i read about the “Artifact Flail” in the Warband Selection Screen and. IT WAS THE PROBLEM. It legit fixed the issue and saved my launch 