Unreal Engine C++ project fails to open (UE 5.6) – DLL errors at startup despite successful build

Development Programming & Scripting
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Hello,

I’m posting here because I’m dealing with a blocking issue with an Unreal Engine C++ project, and despite many checks and attempts, I haven’t been able to clearly identify the root cause.

The project is called TraitreMonde1. It is a C++ project (not Blueprint-only) running on Windows, currently using Unreal Engine 5.6.
The project was working correctly before, but stopped opening after system-level issues occurred on the machine.

Initially, Unreal was showing a pagefile system error. After investigating, this turned out to be a Windows issue related to disk space management and virtual memory configuration.
This has since been fully fixed on the Windows side, and the operating system is now stable again.

Since then, however, the project no longer opens at all.
When attempting to open it, Unreal displays the following message:

“TraitreMonde1 could not be compiled. Try rebuilding from source manually.”

In practice, the Unreal Editor does not start, whether launched from the Epic Games Launcher or directly, and the project seems to fail very early during startup, sometimes without any visible crash.

Looking at the Unreal logs (Saved/Logs), the only errors reported are:

Failed to load 'aqProf.dll' (GetLastError=126)
Failed to load 'VtuneApi.dll' (GetLastError=126)

After checking, these DLLs are related to Intel VTune / profiling and appear to be fairly common and normally non-blocking. I couldn’t find any other explicit errors (no fatal error, no crash reporter).

One confusing aspect is that the project builds successfully in Visual Studio:

  • successful build in Development Editor / Win64

  • target: TraitreMonde1Editor

  • no build errors

Despite this, Unreal Editor does not launch, which suggests the issue happens during the runtime/editor startup phase rather than at compile time.

Here is a summary of what I’ve already tried:

  • fully fixing the Windows pagefile configuration

  • checking available disk space

  • clean reinstallation of Unreal Engine

  • recent clean reinstallation of Visual Studio

  • deleting generated folders:

    Binaries
Intermediate
DerivedDataCache
Saved
.vs

  • regenerating Visual Studio project files from the .uproject

  • successful manual build in Visual Studio

  • verifying the Unreal Engine version associated with the project

  • attempting command-line launches (-log, -NoSplash, -d3d11, -vulkan, etc.)

  • testing Unreal launch both with and without the project

At this point, I’m considering several possible causes:

  • a specific Unreal Engine 5.6 bug or regression

  • a runtime incompatibility related to a C++ module or plugin

  • a GPU driver or rendering backend issue

  • a desynchronization between Unreal Engine, Visual Studio, and the Windows environment after the initial system errors

  • or the project becoming unstable as a result of those system-level issues

My goal is to understand whether the problem is coming from Unreal Engine itself, Windows, or the project, and whether there is a reliable way to repair it, or if it would be safer to create a fresh C++ project and migrate the content.

I can of course provide:

  • full Unreal logs

  • exact Visual Studio error messages

  • detailed versions of Unreal Engine, Visual Studio, Windows, and GPU drivers

Thanks in advance to anyone willing to take the time to read this and share any insight or experience.

2

the issue seems to be with something from intel called VTune, i think you have to manually adjust the DefaultEngine.ini file to disable it.