Where is your WoW folder located? It may just not be finding the folder properly.
On Windows 7 and Vista it Belongs in
Code:
Users/Public/Games/World of Warcraft
On Windows XP it belongs in
Code:
Program Files/World of Warcraft
This is a very rough guess, but I can't think of any other blatant reason why the install should fail.
Hope this helps
-Haith
[Edit]: You also want to make sure the World of Warcraft folder and all of the files in the folder are named properly.
As well, I see you play a french client, but downloaded an enUS one. This is likely where the problem lies. Move your enUS WoW folder into the same directory as your french client. Temporarily rename your french client folder, and name the enUS folder World of Warcraft.
The installer likely isn't able to find your enUS client, due to the fact that the french client is in it's place.
(Granted my theory is correct)