This error message can indicate that there is a corrupted file in the Epic Games folder. Delteing these folders then launching the game again should fix the error. The folder and files inside are recreated when the game is launched again.
Close the Epic Games Launcher:
- In the lower right corner click on the chevron icon (the arrow pointing up)
- Right-click on the Epic icon in the pop-up window
- Select Exit
Delete the Epic Games folders:
- Hold the Windows key on your keyboard
- Tap the R key, this will open a run window
- Type %localappdata%
- Press the Enter key, this will open File Explorer
- Right-click on the EpicGamesLauncher folder
- Select Delete
- Right-click on the FortniteGame folders
- Select Delete
- Try launching Fortnite again