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League of Legends error

"Another instance is running": the old League client never closed

League clientLaunch

The message

Another instance is running

What it means

You closed League, but LeagueClient.exe didn't shut down with it. The new launch sees the old process and refuses to start a second copy.

What to try first

Open Task Manager, end LeagueClient.exe, and launch League again.

Is it you or Riot? If lots of players are hitting this at once, it's probably the servers. Check League server status before you start reinstalling things.

Why League thinks it's already open

It's a bug Riot knows about. According to its known-issues page for the updated client, LeagueClient.exe can hang on after you quit a game, taking a while to close (sometimes long enough that you've already clicked Play again). Relaunch inside that window and League refuses.

Waiting works, eventually. Ending the process yourself takes a bit less patience.

How to clear it

  1. Press Ctrl+Alt+Delete and open Task Manager.
  2. Find LeagueClient.exe, right-click it and choose End task.
  3. Open League again.

If it isn't on the first screen, switch to the Details tab (no tabs at all means you need to click More details first). Riot's article on its newer League patcher names the processes that tend to linger after a game. End any of these that turn up:

  • League of Legends.exe
  • LeagueClient.exe
  • LeagueClientUx.exe
  • LeagueClientUxRender.exe

That article is about patching (a stray process can hold up an update as well as a launch), so the same cleanup helps on patch day.

A close cousin

Getting past launch and then hitting a login session error instead? Also a leftover client. Riot's fix for that one adds RiotClientServices.exe to the list and has you sign out before ending anything.

Other wordings of the same error

  • League another instance is running
  • LoL another instance is running
  • LeagueClient.exe still running after closing

Source: Riot Games Player Support, Updated Client - Known Issues, updated June 1, 2026. Riot's steps are paraphrased here, not copied; checked September 29, 2026.