If you’re still experiencing this error, locate your system tray and see if you can spot a launcher for the game you’re trying to play. For example, if a game has an intro menu that is effectively outside of the game, nine times out of ten this is a launcher, often minimizing as a separate application in the system tray. There are a number of titles that have game launchers that load alongside the Steam client.
One of the most annoying is when you try to load your favorite game and Steam informs you that it’s already running – when, in fact, it’s not.
Like most gaming platforms, Steam comes with a whole host of annoying bugs that can be a real pain if you don’t know how to resolve them.