Dynamics NAV DotNet Interopability MS Project

Hello there.

I'm currently trying to read an .mpp file from Dynamics NAV 2016 using .NET variables but experience problems while opening the .mpp file. I receive the error message: "The argument value is not valid."
I would be very grateful if someone could provide more details about how to do this.

 I have assigned the variables:
***************************************
AppProject : DotNet Microsoft.Office.Interop.MSProject.ApplicationClass
PjPoolOpen : DotNet Microsoft.Office.Interop.MSProject.PjPoolOpen
sPath : Text C:\Temp\test.mpp

So, I'm insantiating the AppProject and the PjPoolOpen
***********************************************************
AppProject := AppProject.ApplicationClass;
PjPoolOpen := PjPoolOpen.PjPoolReadOnly;

And then I'm trying to open the file:
**************************************
AppProject.FileOpenEx(
  sPath,
  '',
  '',
  '',
  '',
  '',
  '',
  '',
  '',
  '',
  '',
  '',
  PjPoolOpen,
  '',
  '',
  '',
  '',
  '')

Thanks in advance!

Best regards,
Sebastien