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League of Legends Failed to Launch: How to Fix It

1 min read

League of Legends cover image

The error almost always traces back to Vanguard. Riot documents one registry value as the fix, and three checks handle nearly everything else.

"League of Legends failed to launch — something unusual happened" almost always traces back to Vanguard, Riot's kernel-level anti-cheat, mandatory on Windows since 2024. If Vanguard cannot verify the machine, nothing starts.

The registry value Riot documents

Riot's own support article for this error points at a single Windows value:

  1. Press Win+R, type regedit, press Enter.
  2. Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options.
  3. Find DevOverrideEnable and set its value data to 0.
  4. Reboot.

Left at 1, it interferes with the integrity checks Vanguard runs, and the client refuses to launch or update.

Check these before anything drastic

  • Secure Boot and TPM 2.0 enabled in BIOS — Vanguard requires both.
  • A full reboot, not just closing the client. Vanguard's driver loads at Windows startup, so a restart genuinely fixes a lot of these.
  • Antivirus exclusions. Third-party AV flags Vanguard files regularly.

Reinstall Vanguard, not League

Uninstall Riot Vanguard from Windows Apps & Features, restart, then open the Riot Client — it pulls a clean copy. Reinstalling the whole game is rarely needed.