VAC Authentication Error

[Hathcyn]

So I was playing this game with one friend and we played together for a while with no error. Several more of our friends have picked it up and now after playing a few minutes in a group I get booted to single player with the error message "You can't join this game session as it is VAC secured and you haven't been successfully authenticated." When I try to join again it instantly boots me back every time after that. I've looked around on the forums and can't find much. I've restarted, forwarded all the ports, verifying the install files, tried to repair steam, and gone through all my security settings.

Anyone actually fix this problem?

Edit: I've also tried combinations of VAC protected game on/off in the online options with my game and my freinds'.

[SoldierZero]

Iv got nothing, tried so many times trying to fix this, after 4 hours I'm just getting a refund. Not worth the hassle

[𝔇ave]

turn vac off... if everyone has vac off there shouldnt be a problem

[Poppi !!]

Originally posted by SoldierZero:

Iv got nothing, tried so many times trying to fix this, after 4 hours I'm just getting a refund. Not worth the hassle

Not after 4 hours play your not.

[Poppi !!]

Look through this Hathcyn;

https://support.steampowered.com/kb_article.php?ref=2117-ilzv-2837

[Hathcyn]

Originally posted by Ðavз:

turn vac off... if everyone has vac off there shouldnt be a problem

Yea, no that does not fix it. That's one of the reasons it seems like something is just wrong.

[Hathcyn]

Originally posted by _StanleyTweedle_:

Look through this Hathcyn;

https://support.steampowered.com/kb_article.php?ref=2117-ilzv-2837

I actually did not see some of these, I will give it a try. Thank you!