: If you own the game on a platform like Steam or Ubisoft Connect, use the Verify Integrity of Game Files tool to automatically redownload the missing file. Restart Your PC
Your "Vanguard"—the critical loader file—has been arrested by the silent revolutionary guard known as Windows Security. Here is how you stage a prison break to get your game working again. Phase 1: The Prison Break (Restore from Quarantine)
If you own the game on or Steam , use the built-in repair tool:
The most common cause is Windows Defender or other antivirus software blocking the file. Open (search for it in the Start menu). Go to Virus & threat protection > Protection history . Look for a recent entry related to uplay_r1_loader64.dll . Click the entry, select Actions , and then choose Restore .
: Right-click the game in your Library > Properties > Local Files > Verify integrity of game files .