I am trying to follow Set Up and Compile a C++ Project in Unreal Engine | Unreal Engine 5.6 Documentation | Epic Developer Community in Unreal 5.6 However when I parent a blueprint off of a C++ class, save, compile and exit unreal, when I restart it, The blueprint not only is no longer parenteded,giving me the error Blueprint could not be loaded because it derives from an invalid class. Check to make sure the parent class for this blueprint hasn't been removed! Do you want to continue (it can crash the editor) If I try to reparent it it won’t work. I have tried this on MacOS 26 and on a fresh install of 5.6 on Windows 11 with the same error so I am unsure what is happening here
Can you try changing the name of the class and recompiling your C++ project? Make sure it’s something unique just to test it out. Sometimes if you use a class name that already exists in the codebase, UE can do very strange things. It’s happened to me several times. If that’s what it is, then you can try and pick a new name that still suits your project.
Also, make sure that you did a build in Visual Studio BEFORE parenting. Don’t parent a class that was added and compiled while the editor is open. That will only last for the session because live compile substitutes class names until you do a rebuild in Visual Studio. This is an especially common problem with new variables in C++.
Ok, I have made a new project named LearningGame, Made a C++ class called KatGameMode, refreshed project, then opened it. then closed UnrealEditor and built the project in IDE, started Unreal, made the blueprint. BP_KatGameMode. Saved it, then exited and started again. As soon as I try to load BP_KatGameMode I get the error again - Blueprint could not be loaded because it derives from an invalid class. Check to make sure the parent class for this blueprint hasn’t been removed! Do you want to continue (it can crash the editor)?
I just tried this exact series of actions in Unreal 5.5.4, and it worked fine, Unreal 5.6? fails again