LS-0018: Application is still running

This error means that a game you are attempting to play is still running.

If you are getting this error, force quit the game or application using your Task Manager.

Shut down the game via Task Manager

1. Press CTRL+ALT+DEL.
2. Click Task Manager.
3. Click Processes.
4. Find the game that's still running and click on it. (Example below is using Magic: The Gathering Arena)
   
5. Click End Task.
   
6. Relaunch your game.

Note: The above instructions use Windows 10 and may vary on other versions.

Shut down a third-party launcher via Task Manager

Some games use a third-party launcher before they start. If you exit a game that uses a third-party launcher but the launcher doesn't shut down, this might cause the error. Follow these steps to force quit the launcher:

1. Right-click your taskbar, and then click Task Manager.
2. If a launcher is running for a game and you get this error click on the process and click End Task. (The example below is from Civilization VI)
   
3. Launch your game.