Migration problems with 4.11


Since migrating my project to 4.11, I’m facing 2 big problems:

  • One parent class now throws the FixupRootNodeParentReferences() warning and in consequence all the components of children classes don’t show up anymore in the components tab.

I tried everything and even if I delete the root component in the parent class and recreate it, the problem eventually comes back.

  • I have a base class that is used for almost every blueprints but now when I want to compile it the editor crashes with the following error:

Fatal error: [File:D:\BuildFarm\buildmachine_++UE4+Release-4.11\Engine\Source\Runtime\Engine\Private\BlueprintGeneratedClass.cpp] [Line: 131]
UBlueprintGeneratedClass::GetAuthoritativeClass: ClassGeneratedBy is null. class ‘/Engine/Transient.TRASHCLASS_ProtoInteractiveObject_5472’

In this state I’m afraid that my project is absolutely unusable with 4.11 but I really need this version :frowning:


  • Could you provide the logs from your project’s Saved->Logs folder?
  • Are you getting a Crash Reporter window? If so, please provide your Machine ID from the window and ensure that you hit Send on the Crash Report.
  • Also, keep in mind that upgrading projects to newer versions is much more involved than just opening a copy of the project. You may need to recreate entire blueprints in order to get them to function properly in a later version. While this may not be the case with your current issue, it’s good to keep this information in mind.


I attached some of the logs.

Yes I sent error reports a few times. My Machine ID is:

While I do understand that upgrading can be complicated, I think those errors are due to a bug because I had problems with root node references since a very long time and accros every version…



Looking into the crash, there unfortunately is not much information to go on.

Have you been able to reproduce this crash in a clean project at all? It seems project specific, and if that is the case, could you please zip up your project, upload it to Dropbox, and provide me with a link through a PM on the forums? Here is the link: https://forums.unrealengine.com/member.php?160394-Sean-Flint

For the first bug related to the FixupRootNodeParentReferences(), I can reproduce it in a clean 4.11 project:

  • Create an actor blueprint “test”
  • Create a child “test_child” of the test blueprint
  • In the child blueprint, attach a few static mesh to the DefaultSceneRoot
  • When you recompile the parent blueprint, the FixupRootNodeParentReferences warning appears

Thank you for providing the repro steps for this issue. For the FixupRootNodeParentReferences() issue, it already exists in our system as UE-20632, and is currently being investigated by our developers.

As far as your crash goes, have you been able to reproduce that in a clean project as well?

No unfortunatly I don’t think it is possible to reproduce the crash on a blank project.
I sent you a PM on the forum with a link to download the project and investigate the crash.

Thanks for your help.

If your problem is with a particular blueprint, it would be beneficial to attempt to recreate that blueprint from scratch in your project to see if you can get the same crash to occur. It is possible that the asset became corrupted somehow, and that is what is causing you to have issues.

This blueprint is only a base class and there is almost no code in it.
While it is very easy to recreate that blueprint, it is literally impossible to replace it with a new one. When I try to swap it with a new one I have an error “This blueprint is in use”. I tried many times but I don’t see how I can replace it.

When you say you’ve tried to replace the blueprint, did you attempt to delete the original and use the Replace References option?

Yes I tried both deleting the blueprint and using the “replace reference” tool.
In both cases there is an error “This blueprint is in use”.
I tried with the “NoLoadStartupPackages” but it does not change the problem.

After opening your project, I was able to delete the ProtoInteractiveObject BP without any issue. While it did take a minute or two to delete, it completed successfully. Could you try deleting the blueprint one more time (after you recreate it, of course)? The issue seems to lie within that blueprint from what I’ve seen so far.

While deleting the blueprint without replacing references indeed works, it’s useless because the whole project is then broken and I would need to rebuild nearly every other blueprints in the project.

I tried recreating the same blueprint from scratch (first time I duplicated it) and deleting the original one with the “replace reference” but this time instead of the error “this blueprint is in use” the editor crashes instantly without any crash report.
In the log there is this error:

[2016.02.18-09.15.49:388][265]LogWindows:Error: === Critical error: ===
Fatal error!

Crash in runnable thread TaskGraphThread 2

[2016.02.18-09.15.49:390][265]LogThreadingWindows:Error: Runnable thread TaskGraphThread 0 crashed.
[2016.02.18-09.15.49:390][265]LogWindows:Error: HandleError re-entered.
[2016.02.18-09.15.49:390][265]LogWindows: FPlatformMisc::RequestExit(1)


After investigating this issue, it seems to be related to a known issue, UE-26761. This issue is currently being investigated by our developers. I will provide updates as they become available.

Have a great day