Why: This happens when your Windows user name has special characters (e.g., C:\Users\João). Old BeamNG can't read Unicode paths.
Fix: Create a new Windows local user named BeamUser and run the game from there. A pain, but it works.
Once you have successfully downloaded version 0.18, you may encounter issues running it on modern hardware or with mods. Here is how to ensure it works: beamng drive 018 download work
If you own BeamNG.drive on Steam, downloading and getting v0.18 to work is a 3-minute process. Why: This happens when your Windows user name