Game crashes with Error,

Pak file corrupt or tampered with. Please use steam option “verify integrity of game files” to repair game install. Exiting…
I have deleted all mods and reinstalled, kept crashing, deleted the mods and tried to play vanilla kept crashing, removed and reinstalled game, kept crashing, removed game and steam reinstalled both, kept crashing, reformatted HD reinstalled with just game and steam, still crashing. All drivers are up to date. Since this insane error does not list exactly what is corrupt it makes it extremely hard to narrow down ]