Same issue as this ticket which already has been reported here http://feedback.arma3.com/view.php?id=579 ?

I've experienced the same error message in MP sessions playing both over the internet or LAN. However, I've found a solution that works for me and made my Arma 3 Alpha run all stable: Download and install this DirectX End-User Runtime Web Installer (http://www.microsoft.com/en-us/download/confirmation.aspx?id=35). It might work for others having the same issue...

OS: Windows 7, 64 bit