Ensure your startup .bat file uses quotes around the -mod parameter if any folder names contain spaces (e.g., "-mod=@CBA_A3;@ACE" ). 3. The "Steam Sleep" Syndrome
: If you are using a non-dedicated (live-hosted) server, you may encounter this error because it lacks a proper config file to whitelist IPs. Switching to a dedicated server setup—even on the same machine—is often the solution. 2. Check Your Mod List arma 3 headless client steam authentication failed hot