I found a fix!
Im currently using Bullguard antivirus software, and even tho you shut it down, it still have some servies running in the background.
So I totally uninstalled my antivirus, rebooted, and boom. Updated with no problems.
Hope it can help others :-)!
Edited by Bangeall on 31/08/12 05:17 (BST)
I'm going to copy-paste what I wrote in another thread. This soluation posted on the US forums worked for me, but I can see in this thread that it is not working for others; still, there is no harm in trying it and posting whether or not it worked. This issue is cropping up quite a lot in a number of different threads. Perhaps we should get one stickied to draw as much attention as possible to the problem.
1. Click Start and open Control Panel.
2. Go to Appearance and Personalization. Then press "Show Hidden Files and Folders". A small window should open, with a list inside. In that list, be sure to select the "Show Hidden Files and Folders" option again and press Apply.
3. Go to Computer and hit OS (C:).
4. Go into ProgramData. You will see a folder named Battle.net. Delete this.
5. Right-click on the WoW launcher icon and hit "Properties". Make sure you are running WoW as admin.
This solved the issue for me, but I think it would be a good idea for people who are experiencing the same problem to post and highlight the issue, or note if the above did not work for you, or if something else solved the issue for you. I tried everything suggested in the Help section, including Safe Mode, Select Start, disabling my anti-virus, updating Adobe, and uninstalling the game. This was the only thing that worked for me.
After reading many different forums and trying all the suggestions that didn't seem to work, I went trudging through all of the agent log files and finally found out why my WoW client had the issue.
File C:\ProgramData\Batte.net\Agent\Agent.1267\Logs\repair-on-demand.log stated that file wow-update-enGB-14946.MPQ in the my WoW data directory contained an error and was read-only. I investigated to find that such file was not read-only, so I removed the file altogether. Tried again, still an error. The log file now mentioned the same file but in a different directory, so I removed that file as well. Problem solved, client is happily downloading updates.
Naturally each problem may have unique circumstances so I recommend you look through all recently changed log files in the Agent folder and all sub-folders, the problem is likely to be similar. Make sure that agent.exe is not running or you won't be able to access the log file.
Hope this helps.
For OS X Users.
My solution to rid of this error. Simply, move your WoW installation directory to another place.
I was have:
$HOME/wow/Word of Warcraft
when I moved the "Word of Warcraft" folder into the $HOME/Desktop the updater starts working and updated my game.
After the update i moved back the "Word of Warcraft" folder into the
$HOME/wow/Word of Warcraft
and the game again refused to load. So, renamed the "wow" into "blizz" and the game runs ok, so now i have $HOME/blizz/Word of Warcraft.
If you installed the game into "standard" location /Application , simply move it to the ~/Desktop and give a try..