If the game server cannot determine the version of the game you are running, then it will not allow you on, and will say it is "Unable to Validate Game Version."

Reverting the game to a previous version may also assist with the troubleshooting process. In order to revert the game to a previous version, please try the following steps:

1. Open your World of Warcraft directory (This is commonly located at C:\Program files\World of Warcraft)
2. Open the folder called "Data"
3. Delete the Patch.MPQ file
4. Run the repair.exe utility found in the World of Warcraft directory
5. Click the button "Reset and Check Files"
6. The repair utility will say, "World of Warcraft is seriously damaged and will need to be reverted to an earlier version. After it has been reverted you may need to patch up to continue playing."
7. Once the repair utility has completed, you will need to reapply the patch to enter the game.

If that does not correct it, uninstall the game and reinstall it. In order to make sure you've got the original game data files, we will need you to fully reinstall the game before trying to log onto the game servers again. After fully uninstalling the game and removing the game directory from the hard drive, please reinstall the game and connect to the game server. It should download the latest patch automatically, and once it has applied successfully, you should be able to log into the game again without error.

If the problem persists, a virus may be altering the game data somehow.
Check our Security Page listed here:
http://us.blizzard.com/support/artic...rticleId=20569