League of Legends · League of Legends on Windows PC
Fix “A Critical Error Has Occurred” in League of Legends
Source-checked · About 15 minutes
Answer
For League's “A critical error has occurred” dialog, close apps that display controls or information over the game, such as Discord, Steam, or NVIDIA's in-game overlay. End any remaining League and Riot Client processes in Task Manager, then open Riot Client > profile icon > Settings > League of Legends > Repair. Test a custom game after the repair. This guide does not apply to a VAN code or a Windows blue screen.
Use these steps when League displays “A critical error has occurred and the process must be terminated.” If the message begins with VAN, Windows itself shows a blue screen, or the Riot Client cannot patch, use the instruction for that exact failure instead.
2
Close apps that display things over League
An overlay is a feature that draws controls, notifications, or performance information over the game. Quit Discord, Steam, NVIDIA or AMD in-game overlays, recording tools, and similar apps. If you want to keep an app open later, turn off only its League overlay. Do not close Windows security processes.
3
End the stuck Riot session
Press Ctrl + Shift + Esc to open Task Manager. End League of Legends, LeagueClient, LeagueClientUx, and RiotClientServices if they are still listed. Wait until those entries disappear before opening the Riot Client again.
4
Repair League's installed files
Sign in to the Riot Client, select the profile icon in the upper-right corner, choose Settings, select League of Legends, then choose Repair. Leave the client open until the repair finishes; do not delete the Config or DATA folders while it is working.
5
Retest in a custom game
Start a custom game with the overlays still closed. Success means the loading screen opens, League reaches the map, and the critical-error dialog does not return during the same action that triggered it before.
6
Collect logs if the error returns
Run Riot Repair Tool as administrator, choose League of Legends, and let it create a ZIP file. This file packages technical logs that help Riot diagnose the crash. Attach it to a Riot Support ticket with the full dialog text, the time of the crash, and the name of the last app you turned back on before the error returned.
If it does not work
If League works with every overlay closed, re-enable one overlay at a time and repeat a custom-game launch. The error returning after one re-enable identifies the conflict.
If the critical dialog appears before any match opens, Client Repair is still appropriate; changing in-game graphics cannot help until League reaches the game window.
If the dialog offers to create a crash dump, allow it and keep the file for Riot Support. A crash dump is a technical record of what the program was doing when it failed. Do not upload it publicly because it can contain details about the PC.
ⓘ Sources and verification
Checked against official documentation on . Scope: League of Legends on Windows PC.
Riot's error table associates this exact critical-error dialog with overlay programs. The steps therefore isolate overlays first and use the current Client Repair control before any reinstall.
