What to do when I got "An Unreal process has crashed..." error?

Sometimes after some changes in code I got this error and the only thing I can do is report it to them and I can’t change in my project anymore. Is it possible to return to previous build or something else?

If you’re running the game in a debug editor, directly from visual studio, you can provide Epic a copy of the stack trace. Otherwise, just cancel and restart. Any unsaved changes may be lost when you crash, so stick to the golden rule: save early, save often. If you have source control (Git, etc) you can roll back breaking changes.

You mean something got screwed up in either blueprint or c++ and you try to open your project but it crashes on startup?
Is it because of a C++ error or because of a blueprint error? The crash report should say that. If it isn’t, look in your <ProjectFolder>/Saved/Logs or <ProjectFolder>/Saved/Crashes and take a look at the most recent .log files, it should say there what caused the crash.

If it is a blueprint error and the error report says which blueprint it is, look insice your <ProjectName>/Saved/Backup folder. There UE4 keeps backups of previously saved blueprints. You might want to try and replace the error-causing blueprint with one of the backups (keep in mind though that you might lose some work progress though, since you’re replacing your blueprint with an older version which might not have all the changes you made before the crash occured).

If it is because of a C++ error in your code, you can still open your C++ code via Visual Studio by opening your <Projectname>.-sln file in your project main folder. There you can fix your code and compile it with Build->Build <Projectname> at the top of Visual Studio.

Personally, when i’m done for the day with UE4 i copy my entire project folder to a backup hdd so incase i screw something up during the next day (or my hdd with the project folder dies) at least i can roll back to the previous days state. Services like Git and Github are also a good idea if you want it.