I've got a problem with my WoW installation.
As many people , i had "Your game installation is damaged , please run repair." error in patch day.So i was forced to reinstall the game with my 100KB/s connnection.
After 5 days , i was able to download %75 of game , and im at "Playable" phase.I can launch the game and play normally.
I was happy that finally im able to log in , then i remembered that i need my addons to play , so i downloaded all my addons and installed them.It was alright , i was still able to log in without problems.

But the problem occurred when i tried to copy my old "WTF" folder to WoW directory , when i did that and started the launcher , it went back to "Optimisation" (literally , im starting to hate that thing.) but it made it lightning fast , and proceeded to download 10GB's of data.

I tought that happened because my WTF folder is "old" , so i deleted the folder and started the launcher again.It made another lightning fast "Optimisation" but started from playable phase again.

After i saw that , i logged back in game and decided to manually configure my addons.It had no problem in game , nothing weird happened.Background downloader was downloading from %75 , small latency.Then i exit the game for lunch and when i was back i wanted to play WoW and do dailies.

Guess what happened ?

Another lightning fast "Optimisation" and 10 GB of download.

After i saw that , i closed the launcher , cut the WTF folder , and pasted it to desktop.When i start the launcher , another "Optimisation" process happened but its at "Playable" phase again.

So , something is wrong with WTF folder-Launcher interaction , and i suspect it was the main problem of "Your game installation is damaged." error.

I think , i just gave you enough information to fix that thing.

No Antivirus - Firewall are active.