BC-124 is a common error for Xbox One users and often occurs when a new update is released for Overwatch or Xbox One. If your console or game is out of date, you won’t be able to connect to the Overwatch servers live.
If you’re having this problem, you can try resetting your Xbox and manually checking your settings to update. You can also sign out of Overwatch and check the update queue to see if a new patch is being downloaded.
There was a problem while trying to authenticate with Xbox Live. Please try again later. (BC-124)