Hi Digitalism,
probably your machine doesn't have enough resources for the particular scene.
Here are some advices on how to reduce the VRAM consumption:
To keep the polygons count low, it is very important to enable in c4d the Render Instance, or Multi Instance (R20/R21) option for all the objects that support it, like MoGraph Clonerrs, Instance Objects, or Particle Emitter.
To keep the polygons count low, another trick is to disable all the Subdivision Surface objects in the scene, and apply to them an Octane Object tag, with the same subdivision settings in the proper tab.
In this way, the subdivision will be applied only at render time, and the scene will be much easy to export and handle.
Also 32bit/16bit textures can be reduced to jpg/8bit, to save a lot of space.
Also setting the Imagetexture node to Float/Grayscale instead of Normal/RGBA, for all the Bump/Roughness/Metallic textures, and in general for all grayscale textures, can save up to 3x memory per texture.
Finally, if you reduce the Parallel Samples in the Kernel settings at 1, you can save some VRAM, but also reducing the rendering speed.
ciao Beppe