We really don't support this activity just to use an addon, but this may help.
"Vista/Win7 can also create copies of the game files and folders which can interfere with updates. To begin you will need to be able to view hidden files and folders. To do so, click your Windows/Start button, select 'Control Panel' from the menu, then 'Appearance and Personalization', then 'Folder Options'. Next click the 'View' tab, scroll down the list and look for the option 'Hidden files and folders', make sure this is set to Show hidden files and folders.
Now using your 'Computer' option in your main menu, please navigate to the following location:
C:\Users\*your account name*\AppData\Local\Virtual Store\Program Files
If there is a folder named "World of Warcraft" in this folder, please delete it and then restart the game using the Run As Administrator option.
Account and Technical Services
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