Error: VAC unable to verify your game session

In case you encounter a VAC verification issue.

• Steam -> CSGO -> properties -> betas (chose the newest one "1.38.3.6 - 1.38.3.6") if no download happens, choose demo.
• launch the game. Since I chose demo, I couldn't launch the game.
• close the game
• Steam -> CSGO -> properties -> betas (chose the actual patch "NONE") That works for me, hope it will work for you too! 🙂