A: No. "Steam Validation Rejected" is a connectivity/file integrity error. It is not a VAC ban. If you were VAC banned, you would see a specific notification on your Steam profile and would not be able to join any VAC-secured servers for the game.
Common messages:
A: If this happens on only one server but not others, the issue is likely with that server's configuration, not your game. The server may be running a custom map or a plugin that requires you to download extra content, or the server host may have an outdated or corrupted installation. left 4 dead 2 steam validation rejected