I've been having the same problem since I installed (store bought copy) yesterday. Keeps saying one file failed to validate and will be reaquired, steam (supposedly) does that, or says it does, then when I validate the game again, the same thing happens. Don't know how to fix it. I've installed/reinstalled 3 times, deleted the cache and all files for DS3, reinstalled again, and the same problem. When I try to play, I get a message saying the game has to close, sorry for the inconvenience, and that's it.