This error is caused by the scene requiring more RAM than you have available. Indigo has been tested with scenes up to 30 million unique triangles and creating images bigger than 10 megapixel - but if you do run out of RAM - there are several steps you can take to address this:
Improve your pc:
1. Ensure you are running a 64 bit operating system (32-bit Windows can only allocate 2GB of memory to Indigo)
2. Buy more memory. Indigo works great with 4, 8 or 32GB of ram
3. Don't try and run multiple renders concurrently
Change the scene:
1. Decrease the Supersample factor.
2. Turn off Aperture Diffraction. This feature uses a substantial amount of memory.
3. Decrease the amount of light layers. Each layer contains enough memory for a whole image.
4. Render at a smaller resolution.
5. Downsample the textures you use
6. Simplify the geometry of your scene
7. Use instancing. With instancing Indigo can render literally trillions of triangles in a scene.