This error occurs if your PC doesn't meet the system reqs for the game of if you are having connection issues, id recommend doing the following.
1. Ensure that your computer meets the minimum system reqs for wow.
2. Update your drivers and operating system.
3. Reset your user interface to make sure your files and addons are not corrupted.
3. Reset your network devices
4. If you are not using an ethernet cable, optimize your internet connection to prevent connection issues.
5. Close all other apps to resolve software conflicts.
Hopefully this helps, this is what Bliz recomends to do when you get that code on retail.