It seems Diablo 3’s technical troubles just won’t end. Either Blizzard has overly underestimated the load the game would be experiencing or players have been outright lying for 30 pages on the forums according to Ubergizmo, but players can’t login to serves to play Diablo 3 due to Error 73.
Error 73 is described as “a message that appears when the servers are down”. Simply put, when you have millions of players logging on, sooner or later you’re going to experience server capacity issues. When the server just can’t take anymore, it sends out the message thus preventing further logins.
Hilariously, Error 73 was one of the key issues facing Diablo 3 when it launched in May. And why not? When you have the much anticipated sequel to one of the most popular gaming franchises for PC coming out, server overloads are to be expected.
Of course, since you need to login to be able to play Diablo 3’s single-player, such problems effectively lock players out of the game, which further lead to questions as to why a single-player experience needed constant online access (after all, it was one of the issues that sounded the death-knell for Ubisoft’s DRM).
As of now, Blizzard has not addressed the issue.
Source: GameNGuide