hi @NoHoldsBarred ,
The error is due to part of an update not successfully completed. Part of your update is missing, usually due to a transient network error.
This often happens in Windows 11 make sure you have enough free space on disk first
You will need to verify your UEFN installation as in past post
If this does not work try deleting files in Windows File Explorer path
C:\Program Files\Epic Games\Fortnite\FortniteGame\Content\Paks
next of into Epic Launcher as in the link above and try Verify again
If you tried to load in UEFN before 1200 GMT the final pack on my Windows 11 was deleted
If that does not work you will uninstall UEFN and reinstall using the same post picture