i can't do a screenshot (don't know how) but i copied the text:
An error was detected while verifying the contents of the file "C:\Program\World of Warcraft\Data\expansion.MPQ". There may be a problem with your system, or with the drive at C:\. You can attempt to install again. If this problem persists, please contact Blizzard Technical Support.
To check this installation for problems, click the "Repair" button. The Repair tool can automatically fix many update errors.
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I used the repair tool but it said something about a connection to server failed or something like that