For anyone else who might get this after reinstalling windows and UE4.
Copy “UnrealVersionSelector.exe” from your directory :
…\Program Files (x86)\Epic Games\Launcher\Engine\Binaries\Win64
Paste that into …\Program Files\Epic Games\UE_.**\Engine\Binaries\Win64 where (UE_.** = version of UE4 you need to have your uproject launch from)
Launch UnrealVersionSelector.exe
That should give “Registration Successful”.
That’s it!
Go back into the Launcher and Launch your project.