Error code 901 in Roblox is an authentication error that usually appears for players on Xbox. The error message may indicate that the user account connected to the Gamertag is moderated. One possible solution is to review the moderation status by logging in on any other device, such as a web browser or mobile device. Other solutions include restarting Roblox a few times, checking for important updates that havent been installed yet, and following the steps recommended by Microsoft. A video on YouTube also provides solutions for fixing the error.