[4.6 Upgrade] blueprint parent classes gone


after some renaming and updating to 4.6 basically all of the parent classes of my blueprints are totally messed up or gone, but I can’t edit them in the editor because of the invalid base class -.-
Is there any way to edit just the base class of the blueprint … ?
Thanks in advance for any help, I’m really stuck and annoyed here, I’m not gonna redo that ton of blueprints


Hi ,

Do you mean that all of the children of your parent blueprint are giving errors? What error are you getting in the parent class?

Hey ,
I just can’t open the Blueprints anymore… When I attempt to open them (via the Editor) I get this 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.

The problem is, most of my Blueprints show me (when hovering about them in the Content Browser) that their Parent Class is None now (how did that even happen? Even standard stuff like UMG-Widgets that I just derived from the base classes given by the engine) and I can’t really do anything about that as it doesn’t let me edit their parent classes :frowning:

Thanks for your comment!

Were you able to open them in 4.5? Additionally, if you migrate the parent blueprint to a new, blank project are you able to open it there?

Yes, I created them in 4.5 (and therefore openend / edited them) but I guess there was an error somewhere when upgrading to 4.6, as the parent class is still None, even after migrating (well, how should that new project know the true base class :wink: )
Is there any way to manually reparent a blueprint ?

Hi ,

I meant that you should migrate the base class to a new project, I apologize for the miscommunication. Try migrating that to see if you can open it. Additionally, while adjusting, did you move any of your files to new folders? It could be that the references broke and you need to manually re-reference the parent class for it to be able to work.

Mhh I didn’t move any files :confused:
Let’s take the UMG-Widgets for example, they derive from UUserWidget, right? I can’t migrate that UUserWidget as its part of the engine …

My setup was basically like this:

Engine Classes (Actors/Objects) → my own derived c++ classes (AMyCustomActor derived from AActor f.e.) → blueprints that derive from those c++ classes (AMyCustomActorBP derived from AMyCustomActor f.e.), but also blueprints like UMG-Widgets (MainMenuWidgetBP) that skip the custom c++ classes part, like my menus and directly derive from classes from the engine (from UUserWidget f.e.)
Both types of blueprints are gone, so I’d need to find a way to re-reference them, as the base-classes are definitely there, the blueprints just don’t know them.

Sorry, if I misunderstand something here :frowning:

Do you have a copy of the project that you would feel comfortable sharing? I would be happy to take a look if you upload it to a trusted FTP server such as dropbox and message the link to me on the forums.

I cannot show you those files anymore, as the parent classes magically reappeared (???), now the parent classes for all blueprints are correct again. (It says UMG.UserWidget now for my UMG widgets as parent classes instead of None)
I do not really know what happened, but some iterations migrating and reopening and verifying somehow fixed the problem …?
Thank you for your help anyways, if I manage to reproduce the None-Parent-Class-problem I’ll let let you know :slight_smile:

Thank you very much! (if you change your comment to be a reply, I can mark it as answer (or maybe you can even do that yourself? Not sure about Staff rights here :wink: ))

Hi ,

I am happy to hear that you have been able to resolve this error. I will mark this as accepted for tracking purposes, if the problem persists please feel free to post a comment and we will continue trying to discover what is occurring.