This error is usually caused by a hardware problem on your computers, such as RAM, your hard drive, or an overheated processor.
However, this error can also appear if your computer is unable to read a specific file in your game folder.

• Launch the Firestorm launcher,
• Choose your expansion and go to your full client folder and select it.
• Select "Settings" and click on "Analyze and repair"
  
• Wait for the repair to be completed,
  
• Click on the "Play" button
  

• Check the status of your hard drive and close all programs in the background.
  

• Try to reinstall the game.