Creating instance of the COM component with CLSID {..} from the IClassFactory failed due to the following error 800a0005 CTL_E_ILLEGALFUNCTIONCALL

Question

My web API (c# .net 4.7..), hosted on IIS (Windows 10), in order to run properly, requires a piece of software installed on the PC where the IIS is. This piece of software is written in VB and it needs to be running in order for the web-API to start up properly. The web API is referencing some VB functionality via interop and COM registered dlls.

In Task-manager, i observe that IIS\worker process instead of referencing my running VB6 process, starts a new instance of the VB software (but not properly - and some variables are not loaded in this second instance - i assume this) hence i get the following error:

Creating an instance of the COM component with CLSID {...} from the IClassFactory failed due to the following error: 800a0005 Exception from HRESULT: 0x800A0005 (CTL_E_ILLEGALFUNCTIONCALL).

I have configured IIS and the app pool identity and authentication so that IIS/worker process is starting as the same user as the VB software is run as (both elevated).

I am not sure on how to force the w3w worker process to see the already running VB exe and prevent it from running a new instance of it.

When I am developing in visual studio 2019, and the web API is run via IIS express, everything works fine.

Thank you