failed to lauch editor ue4 but not ue5

Development Platform & Builds
1

Hi Everyone,

I work on a UE4.27 project from 3 years now.

My desktop (Alienware 2022) is always update for win and all soft and driver.

I have install the WIN update on 2025-11-05 at 18:30 UTC +1 (Geneva, Switzerland)

No launch ue4 for 2025-11-06 because i was a little cold.

And today on 2025-11-07 when I would like relauch my ue4 project : NOT POSSIBLE TO LAUCH UE4 PROJECT. Not from Epic Games Laucher Not directly on win file

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But UE5 is ok ! I can lauch project from epic lauch and directly from win files

and most disturbing, when I lauch directly button 4.27.2 for star a new project it is ok the new project launch and when i will open my project via another ue4 new project it’s work !!!

An other people have this probleme ?

Is it possible to have a ue staff help ?

It is a commercial game begin 3yrs, I have all backup but no one lauch !

Thanks for help and sorry if it is just a little bug

Regards,

Karim Spinedi
Independent video game developer
Geneva
Switzerland

2

This solution worked for me. You’d find UE4Editor.exe under C:\Program Files\Epic Games\UE_4.27\Engine\Binaries\Win64 (or whatever other directory you installed it in)

3

I’ll try, thanks @jakayaki

4

This will fix it, but if you do this you won’t be able to open any UE5 projects until you change the default back. In Windows you can only have one default program per file type, so that means if you use both engines this is not an option, you’ll have to manually open with the editor it’s supposed to open with every single time.

5

Ah I didn’t throught to that @AerixArtGames Thanks for the warning.

For moment, I use my own soluce : click on Engine 4.27 for creat a new project and lauch last (mine It work for moment. I don’t know if it is the best or worst but work to much, 3y, for expect passing to ue5 before 18 month to release [if I respect dead line and planning]… thanks for all !