0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF

[NoobFullStack]

I need some help, as I'm struggling to build the Unreal Engine 4 from source using Visual Studio 2017. I'm getting an error AFTER the build. So when I press F5, things are being loaded and after a minute I receive the following error:

'UE4Editor.exe' (Win32): Loaded 'F:\FleX_Gamedev\UE4-GameWorks-4.19.2-master\Engine\Binaries\Win64\UE4Editor-XMPP.dll'. Symbols loaded.

Exception thrown at 0x00007FFF54C74FA3 (UE4Editor-XMPP.dll) in UE4Editor.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.

Unhandled exception at 0x00007FFF54C74FA3 (UE4Editor-XMPP.dll) in UE4Editor.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.

Does anyone know how to handle this issue? I'm trying to build UE4 including the Nvidia Flex.. So I tried various UE4 + Flex source codes from the official github repo's, and after that, even only the UE4 repo without Flex.. All of them, resulting in exactly the same error..

I'm using Windows, building 'Developer Editor' and Win64 all as instructed in the UE4 build from source.

Any thoughts on this issue?