Search in
Sort by:

Question Status:

Search help

  • Simple searches use one or more words. Separate the words with spaces (cat dog) to search cat,dog or both. Separate the words with plus signs (cat +dog) to search for items that may contain cat but must contain dog.
  • You can further refine your search on the search results page, where you can search by keywords, author, topic. These can be combined with each other. Examples
    • cat dog --matches anything with cat,dog or both
    • cat +dog --searches for cat +dog where dog is a mandatory term
    • cat -dog -- searches for cat excluding any result containing dog
    • [cats] —will restrict your search to results with topic named "cats"
    • [cats] [dogs] —will restrict your search to results with both topics, "cats", and "dogs"

Crash on load - SkeletonGeneratedClass is null

After upgrading to 4.2, my project now crashes on load. The only relevant log line is:

[2014.06.05-03.34.49:609][ 0]LogWindows:Error: appError called: Assertion failed: Blueprint->SkeletonGeneratedClass != NULL [File:D:\BuildFarm\buildmachine_++depot+UE4-Releases+4.2\Engine\Source\Editor\UnrealEd\Private\Kismet2\BlueprintEditorUtils.cpp] [Line: 2906]

I've narrowed the culprit down to one particular blueprint, if it's removed the project loads fine. The project also works perfectly as-is in 4.1.1 and the only change here is the presence/absence of this blueprint. The issue is that this blueprint is pretty large and complex so recreating it or stripping parts out at random to see if something makes it work would take a very long time. Is this error familiar or is there a best way to debug an issue like this?

Product Version: Not Selected
more ▼

asked Jun 05 '14 at 03:53 AM in Bug Reports

avatar image

121 6 8 14

avatar image [Epic] Gribbs ♦♦ STAFF Jun 05 '14 at 01:42 PM

Hey dbc211,

Thank you for reporting the issue that is occurring for you in UE4. If possible, could you please share the Blueprint with us so we could further investigate your issue. Could you also provide your logs, dxdiag, and callstacks from the project so we can look into those as well.

Thanks and have a great day!

avatar image sandboxgod Jun 05 '14 at 01:51 PM

I get that crash when I open one of my blueprints. It derives from a C++ class so not sure if I can share the blueprint.

I'll see if I can repro the crash on a blueprint that is not derived from a custom native class later

Crash dump (part of it):

 UE4Editor-Core.dll!FDebug::AssertFailed(const char * Expr, const char * File, int Line, const wchar_t * Format, ...) Line 160    C++
  UE4Editor-UnrealEd.dll!FBlueprintEditorUtils::GetClassVariableList(const UBlueprint * Blueprint, TArray<FName,FDefaultAllocator> & VisibleVariables, bool bIncludePrivateVars) Line 2907    C++
  UE4Editor-UnrealEd.dll!FKismetNameValidator::FKismetNameValidator(const UBlueprint * Blueprint, FName InExistingName) Line 95    C++
  UE4Editor-KismetCompiler.dll!FKismetCompilerContext::ValidateVariableNames() Line 383    C++
  UE4Editor-KismetCompiler.dll!FKismetCompilerContext::CreateClassVariablesFromBlueprint() Line 438    C++
  UE4Editor-KismetCompiler.dll!FKismetCompilerContext::Compile() Line 3045    C++
  UE4Editor-KismetCompiler.dll!FKismet2CompilerModule::CompileBlueprintInner(UBlueprint * Blueprint, bool bPrintResultSuccess, const FKismetCompilerOptions & CompileOptions, FCompilerResultsLog & Results, TArray<UObject *,FDefaultAllocator> * ObjLoaded) Line 125    C++
  UE4Editor-KismetCompiler.dll!FKismet2CompilerModule::CompileBlueprint(UBlueprint * Blueprint, const FKismetCompilerOptions & CompileOptions, FCompilerResultsLog & Results, FBlueprintCompileReinstancer * ParentReinstancer, TArray<UObject *,FDefaultAllocator> * ObjLoaded) Line 159    C++
  UE4Editor-UnrealEd.dll!FKismetEditorUtilities::GenerateBlueprintSkeleton(UBlueprint * BlueprintObj, bool bForceRegeneration) Line 428    C++
  UE4Editor-UnrealEd.dll!FBlueprintEditorUtils::RegenerateBlueprintClass(UBlueprint * 
avatar image sandboxgod Jun 05 '14 at 01:59 PM

link text Okay here is one of my blueprints that crashes on me. It derives from a native class though. However, the native code is just a stub. I included it as well just in case. In the meanwhile I am thinking I should rollback my project to 4.1.1. Luckily I backed it up. I have a bunch of other blueprints that crash too if that can help track this down

avatar image dbc211 Jun 05 '14 at 04:49 PM

Here's mine for comparison, though it's substantially larger than sandboxgod's.

[1]: /storage/temp/7823-bp_playercharacter.zip

avatar image [Epic] Gribbs ♦♦ STAFF Jun 05 '14 at 08:42 PM

hey sandbox,

I am having an issue trying to open the Blueprint. It is claiming that the blueprint is trying to reference a parent class that we do not have. What parent class is the blueprint derived from? I would need this to open your blueprint.

avatar image [Epic] Gribbs ♦♦ STAFF Jun 05 '14 at 08:58 PM

Hey dbc211,

Could you please share your logs and callstacks with us so we can check those as well. I know that you have shared the one line but if you could share the whole log file, that would better assist us to help with the issue.

Thanks for your patience!

avatar image dbc211 Jun 05 '14 at 09:48 PM

Attached is my log, dump, and dxdiag. Thanks for looking into this!

Sandboxgod, I tried to open your blueprint as well. I added the native parent class to my source and got it to compile after some editing but the BP still claimed to have a bad parent. Might be worth posting another.

[1]: /storage/temp/7853-logs.zip

logs.zip (100.8 kB)
avatar image sandboxgod Jun 06 '14 at 10:52 PM

Crap, all of my blueprints derive from a native class. But yeah, I attached all the sources you should have needed to open the blueprint.I think that is the bug- it cannot find the parent class in 4.2. In 4.1.1 this was working perfectly. Hopeful for a fix! In the meanwhile I have to go back to 4.1.1 I don't know the blueprint code well enough to fix :(

avatar image sandboxgod Jun 06 '14 at 01:28 AM

Okay that Blueprint opens for me if I go through my project and open all the base blueprints first, compile the ones that have a 'compile' sign. Currently my game crashes though when I try to run. Also noticed when I reopened the editor if I don't repeat those steps I'll crash when I attempt to open that blueprint I attached.

avatar image Clapfoot Jun 09 '14 at 08:21 PM

We are also hitting this bug when trying to upgrade to 4.2.

It seems to be related to using a hierarchy of BP-only classes because deleting the leaf classes got rid of the crash.

We're reverting back to 4.1.1 for now. I've attached minidump and dxdiag files in case they are helpful.

minidump dxdiag

avatar image [Epic] Gribbs ♦♦ STAFF Jun 09 '14 at 08:42 PM


Could you please provide the crash logs you are getting with the new crash when you try and run?


Thank you for your information. We will use your information provided to further investigate the issue also.

Thanks all for your patience!

avatar image Tim C ♦♦ STAFF Jun 09 '14 at 10:42 PM


I spent a little time today trying to reproduce this issue and have so far been unsuccessful. I created several projects in 4.1.1 using a series of Blueprints derived from one another, some from a base Blueprint and some from a C++ base class, then upgrading the projects to 4.2.0 and I did not run into any problems with opening the project in 4.2.0.

Here are the steps that I was following:

  1. Create new project in 4.1.1.

  2. Create new Blueprint (BP1) either in the Editor or from new C++ class added to the project.

  3. Create new Blueprint derived from BP1 (BP2).

  4. Create two new Blueprints derived from BP2 (BP3 & BP4).

  5. Create new Blueprint derived from BP3 (BP5).

  6. Upgrade project to 4.2.0.

I also tried including the Blueprints that were provided by some of you and derived several new Blueprints from those, but still had no issues when upgrading to 4.2.0.

Would you be able to provide any additional information about how you are setting up your Blueprints? Can you make this issue happen in one of the template projects, or has it only happened for you when upgrading your own projects to 4.2.0? Any information you can provide to help us track this down would be greatly appreciated.

avatar image sandboxgod Jun 10 '14 at 03:41 AM

Blueprint crashes on 4.2 Just uploaded another blueprint. This one does not extend a custom native class so hopefully you can reproduce the crash with this one. If not, I can send you Epic devs a link to my project (I probably will anyway just in case).

avatar image dbc211 Jun 10 '14 at 03:43 AM

I was able to create a brand new 4.2 project, insert a combination of blueprints, and cause the crash reliably. The crash only seems to occur when all of the attached blueprints are in the project - if any one of them is missing, no crash. Just copy the attached folder into the Content of a new project, start it, and try to open the blueprint BP_PlayerCharacter. You should get the crash then.

The blueprints all have references to each other and three of them form a BP hierarchy, so it's very difficult to narrow down further what the problem is here.

[1]: /storage/temp/8156-blueprints.zip

blueprints.zip (334.3 kB)
avatar image sandboxgod Jun 10 '14 at 03:58 AM

Good job dbc I think you nailed it! I just repro'ed the bug using those exact same steps!

avatar image Tim C ♦♦ STAFF Jun 10 '14 at 02:50 PM


Using the files provided by dbc211 I was able to recreate the issue. I did not see a crash event when loading the project, but whenever I tried to open one of the Blueprints that you provided the Editor would crash, so we are making progress. I was also able to open all of the Blueprints in a 4.1.1 project without any problems. I will give this information to a Developer for further investigation. We really appreciate your patience and help with this issue.

Thanks, Tim

avatar image dbc211 Jun 10 '14 at 02:56 PM

The crash on project load was because the broken BP(s) were referenced by the default map, so they were trying to compile on load. Thanks for your help!

avatar image sandboxgod Jun 10 '14 at 08:17 PM

Yay! Please let us know when you submit a fix. I can integrate the change and upgrade to 4.2 when it is ready :D

avatar image Funkenstein Jun 11 '14 at 04:17 AM

I think this fix went into the 4.2 branch yesterday. Submitted as "[INTEGRATE] Change 2098168".

I re-downloaded the source, rebuilt and now I don't get any crashes on load. Not sure if this will fix your issue but might be worth giving it a shot.

avatar image sandboxgod Jun 12 '14 at 09:58 PM

Awesome thanks guys!

(comments are locked)
10|2000 characters needed characters left
Viewable by all users

1 answer: sort voted first

This does indeed seem to be fixed in 4.2.1, the hotfix being prepared for next week. I built the editor from the source and encountered no issues.

more ▼

answered Jun 12 '14 at 07:22 PM

avatar image

121 6 8 14

avatar image sandboxgod Jun 12 '14 at 09:58 PM

Excellent you should set this issue to 'resolved' if you already haven't. I'll checkout the hotfix!!

(comments are locked)
10|2000 characters needed characters left
Viewable by all users
Your answer
toggle preview:

Up to 5 attachments (including images) can be used with a maximum of 5.2 MB each and 5.2 MB total.

Follow this question

Once you sign in you will be able to subscribe for any updates here

Answers to this question