“Internal Mail Database Error” Bug in World of Warcraft

For a while now I have been experiencing an issue with World of Warcraft. My Character puts a lot of items in the auction house and if they expire its a good time to see whether or not its worthwhile to put them into the auction house again, or simply delete them.
While attempting to delete a message which contained an expired auction house item I am always presented with “Internal Mail Database Error”.
I contacted a GM on World of Warcraft about this and they told me to do the following:

1. Disable all Addons
2. Go to the login screen and click “Options”, then “Reset User Options”.

I then restarted the game and again the issue still persisted, so I replied informing that this did not work.
I was shortly contacted via /whisper by a GM who informed me that it was a fail-safe feature on the game gone wrong, and to delete three folders from my program files / blizzard game directory. For safety I saved a backup of these files on my desktop,  I did this and allowed the game to re-create the folders, and restarted the game… the problem still persisted and has not been fixed.
Hopefully they are now aware of this issue, and they might consider fixing this in their next update to the game.