WOW51900322

This error message indicates that there is an issue streaming data to your game client from the World of Warcraft servers. Before trying the following steps, check the BlizzardCS Twitter and Realm Status page for any service interruptions.

1. Ensure the game is up to date. You may need to close and reopen the game. 
2. Reset your user interface to make sure your files and addons are not corrupted.
3. Update your drivers and operating system to resolve any compatibility issues.
4. Reset your network devices to make sure your router hasn't become flooded with data.
5. Update or Modify your security programs, which may mistakenly identify the login module as a security threat.
6. Try creating a new administrator account to resolve permissions issues.
7. The game client may have become corrupted. Uninstall and reinstall the game.

If the previous troubleshooting steps didn't resolve the problem, you can ask the Blizzard player community for help on the tech support forums (if available) or other community gaming sites. Local computer or network technicians may also be able to help if you've exhausted all other resources.