League of Legends Critical Error: Won't Launch Fix (PC)

What is the League of Legends critical error?

The League of Legends critical error appears as a popup reading "A critical error has occurred and the process must be terminated", usually right as the game tries to launch from the Riot Client or just after champion select loads. The client may sit on a black screen, close itself, or never hand off to the game at all. It is one of the longest-running launch issues in League and affects current patches on Windows 10 and 11.

The error is rarely a hardware fault. It almost always comes from corrupted game files, a stale Riot Client lockfile, overlay software interfering with the renderer, or the client lacking the permissions it needs to start the game process.

When does it occur?

• The moment the game tries to launch from the Riot Client
• Right after locking in a champion, dropping you back to the client
• After a patch download or an interrupted update
• Following a Windows update or a GPU driver change
• When Vanguard or the Riot Client did not fully close from a previous session
• On accounts that run the client without administrator rights

Common causes

• Corrupted League game files after an incomplete patch
• A stale .lockfile left behind by the Riot Client
• Overlay software (Discord, Steam, MSI Afterburner/RivaTuner, GeForce) hooking the game
• Outdated or corrupted GPU drivers
• The client running without administrator privileges
• Windows Firewall or antivirus blocking the game executable
• A corrupted Config or Logs folder in the League install

Step-by-step fixes

1. Fully close Riot processes — Open Task Manager (Ctrl+Shift+Esc) and end RiotClientServices.exe, LeagueClient.exe, League of Legends.exe, and Vanguard if present. Relaunch from a clean state before trying anything else.

1. Delete the Riot Client lockfile — Go to C:\Riot Games\Riot Client\Config and delete the file named lockfile (no extension). It is recreated on next launch and clears a stuck session that triggers the critical error.

1. Delete the Config and Logs folders — In C:\Riot Games\League of Legends, delete the Config and Logs folders. League regenerates clean ones on the next start, fixing corrupted settings that cause instant crashes. Your account and skins are unaffected.

1. Run a Full Repair — Open the Riot Client, click the gear icon next to League, and select Initiate Full Repair (Settings > Repair). This scans and re-downloads any corrupted game files. Note: the old standalone Hextech Repair Tool has been retired — use this in-client repair instead.

1. Run as administrator — Browse to C:\Riot Games\Riot Client\RiotClientServices.exe, right-click > Properties > Compatibility, tick Run this program as an administrator and Disable fullscreen optimizations, then Apply. Do the same for League of Legends.exe.

1. Close overlay software — End Discord, Steam, MSI Afterburner/RivaTuner (RTSS), and the GeForce/NVIDIA App overlay. Riot specifically names overlay programs as the most common trigger of this critical error.

1. Update GPU drivers — Install the latest driver from NVIDIA, AMD, or Intel. If a recent driver caused it, use Display Driver Uninstaller (DDU) in Safe Mode for a clean reinstall.

1. Allow League through firewall and antivirus — In Windows Security > Firewall & network protection > Allow an app through firewall, ensure RiotClientServices.exe, LeagueClient.exe, and League of Legends.exe are all checked for Private and Public, and add the Riot Games folder as an exclusion in your antivirus.

If it still doesn't work

If the critical error survives a Full Repair, reinstall just the Riot Client and League rather than wiping everything: uninstall League from Settings > Apps, then download a fresh installer from the official League site — reinstalling the client often resolves a broken core file that repair cannot replace. Also run sfc /scannow and reinstall the Microsoft Visual C++ Redistributables, since missing runtime DLLs can crash the game process on start. If the error only began after a Windows update, check that Riot Vanguard is current, as Vanguard and out-of-date system files frequently clash. For persistent cases, submit a ticket to Riot Support with your client logs attached.