Well, I have done some studies. Very new empty file, 3 walls, viewport saved (the name is Pic2), rendertarget saved to view. 3D-window in AC is opened, Octane is opened, Octane Viewport is opened. Photoreal settings: View Rendertarget is grayed out.
I could understand the logic of setting viewports and using it as Batchrender in Publisher. I used it in AC16 for two months.
If you have any other idea what I mistake, than don´t hesitate to tell me Thanks a lot!