1. Make a copy of the "nvd3dumx.dll" file on your hard drive (if you're using an Nvidia card) and rename it "nvd3dum.dll", then put it into the same folder. Do not alter the original file or rename it.
2. Reinstall WoW, making sure you delete your cache and preferences when you remove it from your system. Third party UIs (User Interfaces) can cause problems on certain systems.
3. Check the temperature of your hardware; overheating can cause the error. Make sure the inside of your case has proper airflow, is free of dust and that all fans are working properly.
4. Update to the latest video and audio drivers available.
5. Close any background applications that are running, such as antivirus programs and chat clients.
6. Stop using any USB sound devices, even if you're not using them in WoW; just unplug them. If that doesn't work, try disabling sound altogether.