I’m just trying to launch the game, but I keep getting this error. It only happens to this particular project. I am able to “Launch” all of my other projects. I was even able to copy the folders from the project I am trying to launch into a new project and I was able to launch that. My question is how do I fix this error in my original project, or can I?
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Still working on it, unable to get it to work so far 
You’ve updated your project from previous version, right? You could try to migrate everything into new blank project, and it should build.
It was an enormous pain for me, when I switched some of the older android projects. It seems, something was drastically changed in the build tools between 17 and 18.
I’ve never updated versions though, which is too bad. I can migrate everything to a new project, it’ll just take a lot of tweaking to get it back to its original state
Huh. That means it’s something else. But migrating to the new project (at least partially) still can be a useful debug tool. Maybe it’s something that you tweaked, that’s causing it. Retracing your steps might help.
Are you working on a C++ project or only BP?
Are you using the compiled version of the engine or the normal one?
Anyway this issue is related with the compile of the engine itself.
You can try to make a normal package (that will compile the engine too) and then try again with the Launcher.
Otherwise, you can make a custom “Launch profile” in which you can set “Build” to true.
I had this same issue when i tried to launch my project on different targets (Consoles for example).
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I’m working only in BP, I have some familiarity with C++ though. I’ll look into this as well.
So, after trying to package the project I learned that 4 filenames were to long. I moved the Project to a folder in my desktop and everything runs smoothly now. I can package and launch 
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Glad it helped!
In-case anyone else finds this - this can also be caused by plugins - FMOD for example - expecting content that does not exist/has not yet been setup. (Like the FMOD sound banks).
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I had this issue with 4.22.3 when switching from a MixedRealtiyHeadset to deployment an Android. I got the error when deploying using the standard “launch to Android” menu option. Using a custom launch profile to rebuild bevor deployment to Android fixed the problem. After this I could use the standdard menu option again.
So I think this is a problem that comes from cached artifacts during the build that get invalid when you switch deployments.
Could you please clarify what you mean by “You can try to make a normal package (that will compile the engine too) and then try again with the Launcher. Otherwise, you can make a custom “Launch profile” in which you can set “Build” to true.”
I tried this and got a new error that says “Error: Unjandled Excpetion: System.Format: Input was not in a correct format”
For me, I had renamed the entire project and project folder. The error output said it was missing [project_name].target. The fix was to go here: C:\Unreal\ [project_name] \Binaries\Win64 & rename the .target file in that folder to the new project name.
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Thank you!! I was getting stage failed error. Using the project launcher worked.
yes it worked for me too! thanks for sharing it
Hi. I don´t even have the .target-file. Should I make one? If yes, how should I do it?
For some reason i didn’t have [project_name]Linux.target file, though i’ve build for Linux many times already. Taking another one *.target file and renaming it helped!
Did you find out how to make a .target file in the end?
Thanks