Okay my UE 4.27.2 was working fine on itself, but after yesterday epic launcher update apparently I was unable to launch any of my projects (this thread here UnrealVersionSelector.exe no longer works with UE4 ) so I was trying to fix this and stupidly decided to run verification of my UE 4.27.2 engine via epic game launcher. It was doing something for a while and succefully finished the verification process BUT NOW I CAN’T EVEN RUN THE UE 4.27 EDITOR ITSELF, I’m getting LS-0013 error - unable to launch Unreal Engine. It suggests to verify the files again, but it doesn’t help. And all of this started after I verified the Unreal files in the first place!
What should I do now, help.
Update: cleared epic launcher cache, reinstalled epic launcher itself, deleted and installed again unreal 4.27.2, and it didnt help.
this is so weird, i started getting the same error yesterday when i try to regenerate my project files, i thought it was something i did. maybe it’s just a coincidence that we got the same error on the same day, idk
now, im trying to build from source and when i run Setup.bat, i get this error:
another update: I’ve downloaded and installed Unreal 5.5.4 (via epic launcher and I never had Unreal 5.5.4 on my computer before) and got LS-0013 error right away when tried to launch the editor.
But then I downloaded and installed Unreal 5.6.1 (once again via epic launcher and I hadnt this Unreal version on my computer before) and it launched perfectly fine.
i got these fixes by asking claude sonnet ai about your issue, i would ask an ai how to fix the issue. Epic has an ai helper on the left side of this page called Developer Assistant:
The LS-0013 error in Unreal Engine typically indicates a licensing or launcher communication issue. Here are the most common fixes:
Quick Fixes (Try in Order)
Restart Epic Games Launcher
Fully close the Epic Games Launcher (check system tray)
Reopen it and wait for it to fully initialize
Try launching Unreal Engine again
Sign Out and Sign Back In
Open Epic Games Launcher
Sign out of your account
Sign back in
Launch the engine
Check Internet Connection
The launcher needs to verify your license online
Ensure you’re not behind a restrictive firewall/proxy
Try disabling VPN temporarily
Clear Launcher Cache (Windows)
Close Epic Games Launcher completely
Navigate to: %localappdata%\EpicGamesLauncher\Saved\webcache
Delete the entire ‘webcache’ folder
Restart the launcher
Run as Administrator
Right-click Epic Games Launcher shortcut
Select “Run as administrator”
Try launching UE again
Verify Engine Installation
Open Epic Games Launcher
Go to “Unreal Engine” tab → “Library”
Click the dropdown next to your engine version
Select “Verify”
Check Windows Credentials
Open Control Panel → Credential Manager
Go to “Windows Credentials”
Remove any Epic Games/Unreal Engine entries
Restart launcher and sign in again
Firewall/Antivirus
Temporarily disable antivirus
Add exceptions for:
EpicGamesLauncher.exe
UnrealEditor.exe (or UE4Editor.exe)
Port 80, 443 (outbound)
Re-associate File Types (If launching from Visual Studio)
Or run this command (replace paths as needed):
“C:\Program Files (x86)\Epic Games\Launcher\Engine\Binaries\Win64\UnrealVersionSelector.exe” /switchversion “C:\Path\To\YourProject.uproject” “4.27”