Valve’s Anti-Cheat System has stopped some players from accessing the multiplayer aspects of Dark Souls 2.
Previous VAC bans against a user’s account has been found to affect the ability to sign in to the multiplayer features in Dark Souls 2. Although news about this is still sparse, numerous threads have been started on the game’s Steam forum complaining about the seemingly indiscriminate banning from servers, even if your VAC ban wasn’t applied for cheating or modding Dark Souls 2.
YouTube user Super Bunnyhop has created a wonderfully informative video describing the issue and past issues with VAC bans. If you have a VAC ban on your account and you don’t yet have Dark Souls 2, I’d urge you to watch this video and decide if missing out on multiplayer features are worth missing out on: