hi @PolyGons67
You will need to delete the file
C:\Program Files\Epic Games\UE_5.4\Engine\DerivedDataCache
Compressed.ddp
This is corrupted and should be rebuilt on restart
If this does not use the “Verify” function to repair from the Epic Launcher
See the 5.4 Installer post
5.4 preview - Development / Getting Started & Setup - Epic Developer Community Forums (unrealengine.com)