Packaging error for windows: Error: Ensure condition failed: FunctionNameFName != FName()

WiseSplinteR · May 15, 2025, 7:16pm

I’m getting this error when trying to package my project. It must be a blueprint that is causing it, but i have no idea which one and cannot seem to find any way to get that information from the error log. I have installed editor symbols, and followed many guides on finding the file causing the problem, with no luck. Is there really no way to get the filename from the cook process when it encounters an error?

Here is the log:

UATHelper: Packaging (Windows): LogOutputDevice: Error: begin: stack for UAT
UATHelper: Packaging (Windows): LogOutputDevice: Error: === Handled ensure: ===
UATHelper: Packaging (Windows): LogOutputDevice: Error:
UATHelper: Packaging (Windows): LogOutputDevice: Error: Ensure condition failed: FunctionNameFName != FName() [File:D:\build++UE5\Sync\Engine\Source\Editor\Kismet\Private\BlueprintCompilationManager.cpp] [Line: 2759]
UATHelper: Packaging (Windows): LogOutputDevice: Error:
UATHelper: Packaging (Windows): LogOutputDevice: Error: Stack:
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb4e690ba9 UnrealEditor-Kismet.dll!FBlueprintCompilationManagerImpl::FastGenerateSkeletonClass'::2’::<lambda_1>::operator()() [D:\build++UE5\Sync\Engine\Source\Editor\Kismet\Private\BlueprintCompilationManager.cpp:2760]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb4e7372d2 UnrealEditor-Kismet.dll!FBlueprintCompilationManagerImpl::FastGenerateSkeletonClass() [D:\build++UE5\Sync\Engine\Source\Editor\Kismet\Private\BlueprintCompilationManager.cpp:3172]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb4e73aebb UnrealEditor-Kismet.dll!FBlueprintCompilationManagerImpl::FlushCompilationQueueImpl() [D:\build++UE5\Sync\Engine\Source\Editor\Kismet\Private\BlueprintCompilationManager.cpp:1018]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb4e739403 UnrealEditor-Kismet.dll!FBlueprintCompilationManager::FlushCompilationQueue() [D:\build++UE5\Sync\Engine\Source\Editor\Kismet\Private\BlueprintCompilationManager.cpp:3472]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb59f51e30 UnrealEditor-CoreUObject.dll!FScopedClassDependencyGather::~FScopedClassDependencyGather() [D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\Blueprint\BlueprintSupport.cpp:486]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb5a218dd2 UnrealEditor-CoreUObject.dll!FLinkerLoad::CreateExport() [D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\LinkerLoad.cpp:5347]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb5a21935b UnrealEditor-CoreUObject.dll!FLinkerLoad::CreateExportAndPreload() [D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\LinkerLoad.cpp:3881]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb5a24048e UnrealEditor-CoreUObject.dll!FLinkerLoad::LoadAllObjects() [D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\LinkerLoad.cpp:4059]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb5a46d3f5 UnrealEditor-CoreUObject.dll!LoadPackageInternal() [D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\UObjectGlobals.cpp:1833]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb5a46b918 UnrealEditor-CoreUObject.dll!LoadPackage() [D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\UObjectGlobals.cpp:2014]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb5a46beb6 UnrealEditor-CoreUObject.dll!LoadPackage() [D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\UObjectGlobals.cpp:1987]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb511b3924 UnrealEditor-UnrealEd.dll!UCookOnTheFlyServer::LoadPackageForCooking() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\CookOnTheFlyServer.cpp:4013]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb511b3b6c UnrealEditor-UnrealEd.dll!UCookOnTheFlyServer::LoadPackageInQueue() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\CookOnTheFlyServer.cpp:2777]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb511c6712 UnrealEditor-UnrealEd.dll!UCookOnTheFlyServer::PumpLoads() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\CookOnTheFlyServer.cpp:2711]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb511f2903 UnrealEditor-UnrealEd.dll!UCookOnTheFlyServer::TickMainCookLoop() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\CookOnTheFlyServer.cpp:1412]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb511f1e97 UnrealEditor-UnrealEd.dll!UCookOnTheFlyServer::TickCookByTheBook() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\CookOnTheFlyServer.cpp:1294]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb50edfe50 UnrealEditor-UnrealEd.dll!UCookCommandlet::RunCookByTheBookCook() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\Commandlets\CookCommandlet.cpp:543]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb50e9f323 UnrealEditor-UnrealEd.dll!UCookCommandlet::CookByTheBook() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\Commandlets\CookCommandlet.cpp:504]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffb50ebdc6f UnrealEditor-UnrealEd.dll!UCookCommandlet::Main() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\Commandlets\CookCommandlet.cpp:243]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ff75781733f UnrealEditor-Cmd.exe!FEngineLoop::PreInitPostStartupScreen() [D:\build++UE5\Sync\Engine\Source\Runtime\Launch\Private\LaunchEngineLoop.cpp:4136]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ff75780cfb6 UnrealEditor-Cmd.exe!GuardedMain() [D:\build++UE5\Sync\Engine\Source\Runtime\Launch\Private\Launch.cpp:140]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ff75780d37a UnrealEditor-Cmd.exe!GuardedMainWrapper() [D:\build++UE5\Sync\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp:118]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ff757810854 UnrealEditor-Cmd.exe!LaunchWindowsStartup() [D:\build++UE5\Sync\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp:258]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ff757826984 UnrealEditor-Cmd.exe!WinMain() [D:\build++UE5\Sync\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp:298]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ff757828eb6 UnrealEditor-Cmd.exe!__scrt_common_main_seh() [D:\a_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288]
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffc27147374 KERNEL32.DLL!UnknownFunction
UATHelper: Packaging (Windows): LogOutputDevice: Error: [Callstack] 0x00007ffc28d3cc91 ntdll.dll!UnknownFunction
UATHelper: Packaging (Windows): LogOutputDevice: Error:
UATHelper: Packaging (Windows): LogOutputDevice: Error: end: stack for UAT
PackagingResults: Error: begin: stack for UAT
PackagingResults: Error: === Handled ensure: ===
PackagingResults: Error: Ensure condition failed: FunctionNameFName != FName() [File:D:\build++UE5\Sync\Engine\Source\Editor\Kismet\Private\BlueprintCompilationManager.cpp] [Line: 2759]
PackagingResults: Error: Stack:
PackagingResults: Error: [Callstack] 0x00007ffb4e690ba9 UnrealEditor-Kismet.dll!FBlueprintCompilationManagerImpl::FastGenerateSkeletonClass'::2’::<lambda_1>::operator()() [D:\build++UE5\Sync\Engine\Source\Editor\Kismet\Private\BlueprintCompilationManager.cpp:2760]
PackagingResults: Error: [Callstack] 0x00007ffb4e7372d2 UnrealEditor-Kismet.dll!FBlueprintCompilationManagerImpl::FastGenerateSkeletonClass() [D:\build++UE5\Sync\Engine\Source\Editor\Kismet\Private\BlueprintCompilationManager.cpp:3172]
PackagingResults: Error: [Callstack] 0x00007ffb4e73aebb UnrealEditor-Kismet.dll!FBlueprintCompilationManagerImpl::FlushCompilationQueueImpl() [D:\build++UE5\Sync\Engine\Source\Editor\Kismet\Private\BlueprintCompilationManager.cpp:1018]
PackagingResults: Error: [Callstack] 0x00007ffb4e739403 UnrealEditor-Kismet.dll!FBlueprintCompilationManager::FlushCompilationQueue() [D:\build++UE5\Sync\Engine\Source\Editor\Kismet\Private\BlueprintCompilationManager.cpp:3472]
PackagingResults: Error: [Callstack] 0x00007ffb59f51e30 UnrealEditor-CoreUObject.dll!FScopedClassDependencyGather::~FScopedClassDependencyGather() [D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\Blueprint\BlueprintSupport.cpp:486]
PackagingResults: Error: [Callstack] 0x00007ffb5a218dd2 UnrealEditor-CoreUObject.dll!FLinkerLoad::CreateExport() [D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\LinkerLoad.cpp:5347]
PackagingResults: Error: [Callstack] 0x00007ffb5a21935b UnrealEditor-CoreUObject.dll!FLinkerLoad::CreateExportAndPreload() [D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\LinkerLoad.cpp:3881]
PackagingResults: Error: [Callstack] 0x00007ffb5a24048e UnrealEditor-CoreUObject.dll!FLinkerLoad::LoadAllObjects() [D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\LinkerLoad.cpp:4059]
PackagingResults: Error: [Callstack] 0x00007ffb5a46d3f5 UnrealEditor-CoreUObject.dll!LoadPackageInternal() [D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\UObjectGlobals.cpp:1833]
PackagingResults: Error: [Callstack] 0x00007ffb5a46b918 UnrealEditor-CoreUObject.dll!LoadPackage() [D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\UObjectGlobals.cpp:2014]
PackagingResults: Error: [Callstack] 0x00007ffb5a46beb6 UnrealEditor-CoreUObject.dll!LoadPackage() [D:\build++UE5\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\UObjectGlobals.cpp:1987]
PackagingResults: Error: [Callstack] 0x00007ffb511b3924 UnrealEditor-UnrealEd.dll!UCookOnTheFlyServer::LoadPackageForCooking() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\CookOnTheFlyServer.cpp:4013]
PackagingResults: Error: [Callstack] 0x00007ffb511b3b6c UnrealEditor-UnrealEd.dll!UCookOnTheFlyServer::LoadPackageInQueue() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\CookOnTheFlyServer.cpp:2777]
PackagingResults: Error: [Callstack] 0x00007ffb511c6712 UnrealEditor-UnrealEd.dll!UCookOnTheFlyServer::PumpLoads() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\CookOnTheFlyServer.cpp:2711]
PackagingResults: Error: [Callstack] 0x00007ffb511f2903 UnrealEditor-UnrealEd.dll!UCookOnTheFlyServer::TickMainCookLoop() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\CookOnTheFlyServer.cpp:1412]
PackagingResults: Error: [Callstack] 0x00007ffb511f1e97 UnrealEditor-UnrealEd.dll!UCookOnTheFlyServer::TickCookByTheBook() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\CookOnTheFlyServer.cpp:1294]
PackagingResults: Error: [Callstack] 0x00007ffb50edfe50 UnrealEditor-UnrealEd.dll!UCookCommandlet::RunCookByTheBookCook() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\Commandlets\CookCommandlet.cpp:543]
PackagingResults: Error: [Callstack] 0x00007ffb50e9f323 UnrealEditor-UnrealEd.dll!UCookCommandlet::CookByTheBook() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\Commandlets\CookCommandlet.cpp:504]
PackagingResults: Error: [Callstack] 0x00007ffb50ebdc6f UnrealEditor-UnrealEd.dll!UCookCommandlet::Main() [D:\build++UE5\Sync\Engine\Source\Editor\UnrealEd\Private\Commandlets\CookCommandlet.cpp:243]
PackagingResults: Error: [Callstack] 0x00007ff75781733f UnrealEditor-Cmd.exe!FEngineLoop::PreInitPostStartupScreen() [D:\build++UE5\Sync\Engine\Source\Runtime\Launch\Private\LaunchEngineLoop.cpp:4136]
PackagingResults: Error: [Callstack] 0x00007ff75780cfb6 UnrealEditor-Cmd.exe!GuardedMain() [D:\build++UE5\Sync\Engine\Source\Runtime\Launch\Private\Launch.cpp:140]
PackagingResults: Error: [Callstack] 0x00007ff75780d37a UnrealEditor-Cmd.exe!GuardedMainWrapper() [D:\build++UE5\Sync\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp:118]
PackagingResults: Error: [Callstack] 0x00007ff757810854 UnrealEditor-Cmd.exe!LaunchWindowsStartup() [D:\build++UE5\Sync\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp:258]
PackagingResults: Error: [Callstack] 0x00007ff757826984 UnrealEditor-Cmd.exe!WinMain() [D:\build++UE5\Sync\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp:298]
PackagingResults: Error: [Callstack] 0x00007ff757828eb6 UnrealEditor-Cmd.exe!__scrt_common_main_seh() [D:\a_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288]
PackagingResults: Error: [Callstack] 0x00007ffc27147374 KERNEL32.DLL!UnknownFunction
PackagingResults: Error: [Callstack] 0x00007ffc28d3cc91 ntdll.dll!UnknownFunction
PackagingResults: Error: end: stack for UAT

brs-sebascova · May 15, 2025, 7:49pm

Hello there @WiseSplinteR!

Checking around the community, and reviewing your log, I believe the line we are looking for is this one:

UATHelper: Packaging (Windows): LogOutputDevice: Error: Ensure condition failed: FunctionNameFName != FName() [File:D:\build++UE5\Sync\Engine\Source\Editor\Kismet\Private\BlueprintCompilationManager.cpp] [Line: 2759]

The error suggests that one of your blueprint functions is not reaching a valid target. As a first step, test by refreshing your nodes, and recompiling all your blueprints. Next, use “Fix Up Redirectors” to check for any possible wrong calls.

If the issue persists, then we would need to pinpoint which blueprint is triggering the issue. As a test, make a backup of your project, then use the copy to delete blueprints one by one, following by a pack attempt.

WiseSplinteR · May 15, 2025, 8:17pm

Hello @brs-sebascova !

Thanks for the reply.

I have already tried the “Fix Up Redirectors” and “Validate Assets” options, with no luck.
I’m not sure how to recompile all blueprints, but i think that happens when you “Play” the project? If so i have already done that and the project runs perfectly in the editor.
I have also opened the blueprints ive worked on recently and compiled them.

I’ll make a backup of the project and try deleting them one by one and package after each. Currently that seems like the best option i have.

I’m surprised that the cook log doesnt specify which blueprint is causing the error! Very frustrating

Thanks again for the help