There is absolutely nothing wrong with the files.
If the files were corrupted on your PC then the launcher would re-download them from the server automatically. If the files were damaged on the server then ALL players would suffer the same issue. They don't.
The issue might be a restrictive windows setting you did (maybe UAC). Or a third party app on your PC trying to run stuff in sandbox. Very hard to tell atm. I don't know your system, your settings or the apps you have installed.
My AV tool since a few weeks also does strange stuff.
When I have played SP (because there I do modding work) and then switch to MP it tells me that files have to be scanned online before I can launch. Takes about 1 minute. Then it tells me that everything is ok and launches the game.
When I launch MP the next time it instantly launches the game without issues.
If I switch back to SP it once again tells me that stuff needs to to be scanned online.
Sometimes security apps do strange crap and even block you from running stuff even if everything is fine.
