This occurs when your PC is put to sleep or hibernation mode and is caused by VAC issue, you can fix it by just turning off your PC and turning it on again and when you launch your game you should not see the error anymore. If that doesn't help disable your antivirus. 

There is one more solution if the previous to didn't help. Close steam, go to CMD (Windows + R > CMD) and put this command in with your steam localisation: 

“C:\Program Files (x86)\Steam\bin\SteamService.exe” /repair.

* Steam has maintenance every Tuesday, if you experience difficulty with the game please wait 10-30 minutes! (There’s nothing we can do to fix it btw don’t ping anyone)