UE 4.9 editor crash when cntrl-w/alt-dragging a blueprint actor

I currently have a blueprint in a simple test level where if i try to duplicate it via cntrl-w or alt-dragging, Unreal crashes. Placing new instances of the blueprint via content browser works without any problems.

my log is as shown:

Unknown exception - code 00000001 (first/second chance not available)

"Assertion failed: (Index >= 0) & (Index < ArrayNum) [File:D:\BuildFarm\buildmachine_++depot+UE4-Releases+4.9\Engine\Source\Runtime\Core\Public\Containers\Array.h] [Line: 678]
Array index out of bounds: 0 from an array of size 0

UE4Editor_Core!FDebug::AssertFailed() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\core\private\misc\outputdevice.cpp:354]
UE4Editor_Engine!USceneComponent::OnComponentDestroyed() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\engine\private\components\scenecomponent.cpp:664]
UE4Editor_Engine!UActorComponent::DestroyComponent() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\engine\private\components\actorcomponent.cpp:944]
UE4Editor_Engine!AActor::DestroyConstructedComponents() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\engine\private\actorconstruction.cpp:163]
UE4Editor_Engine!AActor::RerunConstructionScripts() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\engine\private\actorconstruction.cpp:354]
UE4Editor_Engine!AActor::PostEditChangeProperty() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\engine\private\actoreditor.cpp:113]
UE4Editor_CoreUObject!UObject::PostEditChange() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\coreuobject\private\uobject\obj.cpp:284]
UE4Editor_UnrealEd!ImportObjectProperties() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\editor\unrealed\private\editorobject.cpp:729]
UE4Editor_UnrealEd!ImportObjectProperties() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\editor\unrealed\private\editorobject.cpp:804]
UE4Editor_UnrealEd!ULevelFactory::FactoryCreateText() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\editor\unrealed\private\factories\editorfactories.cpp:793]
UE4Editor_UnrealEd!UUnrealEdEngine::edactPasteSelected() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\editor\unrealed\private\editoractor.cpp:315]
UE4Editor_UnrealEd!DuplicateSelectedActors::FDuplicateJob::DuplicateActorsToLevel() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\editor\unrealed\private\editoractor.cpp:411]
UE4Editor_UnrealEd!UUnrealEdEngine::edactDuplicateSelected() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\editor\unrealed\private\editoractor.cpp:525]
UE4Editor_UnrealEd!FLevelEditorViewportClient::InputWidgetDelta() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\editor\unrealed\private\leveleditorviewport.cpp:2307]
UE4Editor_UnrealEd!FEditorViewportClient::UpdateMouseDelta() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\editor\unrealed\private\editorviewportclient.cpp:1801]
UE4Editor_UnrealEd!FEditorViewportClient::Tick() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\editor\unrealed\private\editorviewportclient.cpp:948]
UE4Editor_UnrealEd!FLevelEditorViewportClient::Tick() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\editor\unrealed\private\leveleditorviewport.cpp:2030]
UE4Editor_UnrealEd!UEditorEngine::Tick() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\editor\unrealed\private\editorengine.cpp:1407]
UE4Editor_UnrealEd!UUnrealEdEngine::Tick() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\editor\unrealed\private\unrealedengine.cpp:366]
UE4Editor!FEngineLoop::Tick() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\launch\private\launchengineloop.cpp:2428]
UE4Editor!GuardedMain() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\launch\private\launch.cpp:142]
UE4Editor!GuardedMainWrapper() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\launch\private\windows\launchwindows.cpp:126]
UE4Editor!WinMain() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\launch\private\windows\launchwindows.cpp:200]


I have a few questions that could help us narrow down the cause of the crash:

  • Can you reproduce this in a clean project?
  • Does it only occur in version 4.9?
  • Could you provide a screenshot of the blueprint that you are trying to duplicate?

Thank you.

Yea, I realized that this bug ONLY occurs for ONE particular blueprint that I had in my system.

I was not able to test in other engine versions as I only have 4.9 at the moment.

The screenshot:

The bad cast is due to the fact that I disabled that node from firing in the fresh project as it was casting to my specific Player character. The editor crashes in BOTH my current project and in a fresh project. (in my current project the nodes are all fully connected)

I believe I am having the same problem, but with 4.10.

For some reason the Editor is crashing when I try to place one of my actor blueprints (called BP_Snow) in any level. Here is one of the crash logs: LOG

The log is saying:

[2015.11.16-23.05.13:520][823]LogWindows:Error: === Critical error: ===
Assertion failed: ChildCount > AttachChildren.Num() [File:C:\UE4\UE410\Engine\Source\Runtime\Engine\Private\Components\SceneComponent.cpp] [Line: 676] 
AttachChildren count increased while detaching 'SecondaryTargetableComponent', likely caused by OnAttachmentChanged introducing new children, which could lead to an infinite loop.

It mentions SecondaryTargetableComponent: one of the CapsuleComponents I add in the constructor of the parent of BP_Snow.

But the weird thing is that I have 2 other actors that derive from the same parent actor, they also have SecondaryTargetableComponent, but the editor doesn’t crash when I place them in the level.

The construction script in BP_Snow is empty, it only calls the the parent’s construction script, and SecondaryTargetableComponent has al it’s default values setted, just like the other two actors I mentioned.

I can stop it from crashing if in the constructor of the parent I remove the following:


But the component shows up in the center of the map (0,0,0), and gets a relative location to the actor from there.

After recreating the Blueprint it’s not crashing anymore. It must have been corrupted or something.

Could you attempt to recreate your blueprint and see if the crash still occurs? As you can see below, recreating the blueprint fixed the crash that Ghar was experiencing, so this may be a solution to your issue since it is blueprint-specific.

I was wrong, after I restarted the editor it crashed again when placing the actor in the level.

I was wrong, after I restarted the editor it crashed again when placing the actor in the level. =( =(

If you are able to provide information on exactly what changes you made before this crash began happening, we can look into this issue further. This issue seems to be related to a blueprint being corrupted, so if there is a way for you to revert to an older version of the blueprint prior to the crash, that is the main suggestion we can make at this time without more solid repro steps.

I have more information. Since I don’t know when the crash started (because I don’t remember the last time I placed this actor in a level), I tried another thing. I was able to make it stop crashing by breaking a reference from another blueprint. I used the reference viewer to see the blueprints that where referencing my “bad” blueprint, started breaking the reference one by one, restarting the editor each time. One of the references did stopped the crash from happening.

The reference I broke was a in function inside a blueprint function library. The weird thing is that I haven’t been using this function anywhere for a while:

I don’t know if this information is useful because I have no idea what this has to do with the capsule component, but I hope it helps.

So I decided to do some testing on my construction script and I found the cause of my crash but I don’t know why (my engine knowledge is potato).

Apparently using the “AttachTo” Node is causing my crash. I tested a number of attachments orders and some of them seem to cause a crash in my editor.

I made an empty actor blueprint and put inside the Const. Script the AttachTo node ONLY (with a cube actor, static mesh actor, and a box collision actor). The following i tested to crash are as follows by putting the actor in the level and trying to duplicate via ctrl-w or alt-dragging:

Target:collisionBox - InParent:cube (common actor) - CRASHES

Target:staticmesh - InParent: CollisionBox - CRASHES

Target:collisionBox - InParent: Static Mesh - does not crash

Target: staticMesh - InParent: CollisionBox - CRASHES

Target:StaticMesh - InParent: Cube (common actor) - CRASHES

Target:Cube (common actor) - InParent:StaticMesh - does not crash

I tested a couple of others which also crashed. Attaching itself to itself does not seem to crash at all (pointless but i was just curious)

I don’t know if I am misusing the AttachTo Node (IE: cannot simply attach certain actors in specific ways) but I just wanted to tell you the extents of my testing.


I have been able to reproduce this crash, and have entered a bug report (UE-23442). Thank you for providing the information and for your report. The only workaround that I have been able to devise at this point is to use the Attach To node in the Event Graph, which doesn’t seem to be causing the crash. If any other workarounds are discovered, please add them to this thread.

Have a great day,

Sean Flint

Same problem

Try upgrading to a later version of the engine. This was an issue that seems to have been fixed in 4.11, so give that a try and see if you’re still seeing the same crash.

Ok, thank you!

I found new issues with!
When i create blueprint and compile it, i had mistake (or this is another bug)
This is lamp blueprint with spot lamp.
I create it from stamdart preset orange lamp blueprint.
I delete point light and drag and droped new spot light from lights menu.
NOW i found that this is incorrect way.
Now i ctrl + c from level, ctrl + v to blueprint! And this is works!

Sorry, this is don’t work! Sorry.