First, try deleting WoW/Cache and WoW/Data/Cache folders.
If that didn't work, try removing or moving out of WoW/Data the wow-update-base-18549.MPQ file. It seems to have different size than what I have on mine, perhaps you have an older version of it.
If still failing, try launching WoW.exe as Administrator.
Ultimately, I would like to see what is going on under WoW/ folder and WoW/enGB/ folder.
If that didn't work, try removing or moving out of WoW/Data the wow-update-base-18549.MPQ file. It seems to have different size than what I have on mine, perhaps you have an older version of it.
If still failing, try launching WoW.exe as Administrator.
Ultimately, I would like to see what is going on under WoW/ folder and WoW/enGB/ folder.