Assistance Requested - "Cannot Execute Boolean Operation"

[CanRobo]

Good Evening Experts!

I could use some assistance on the following blender file. I have created an amalgamation of 3D scans, and spheres to fill in scan gaps. I want to subtract the 2 warped spheres and the “heel” from the mesh called “16835_foot” so that I have a semi hollowed out half-foot. I get everything oriented the way that I require, but whenever I try to do the boolean operation I get the title error.

I truly apologize for the awkwardness of posting a google drive link but I cannot seem to attach the files directly.

https://drive.google.com/file/d/0B7d-HlQvvVp9SVd0V2FBUzBnLUU/view?usp=sharing
https://drive.google.com/file/d/0B7d-HlQvvVp9aVUtcUZCRV9VQkU/view?usp=sharing

This is for a non-profit proof of concept, and any help that you can provide would be greatly appreciated by both myself and maybe a lot of people in need.

Thank you very much.

[Kyriakos]

Hi CanRobo,

to perform a boolean operation you hava to have a clean topology. Your model with the name Sphere has 706 non manifold edges and a lot of inverted normals. Try to fill all the gaps, remove duplicated vertices and invert the normals to the correct direction. If you activete the 3d print add on and press the solid option you will see where the problems are. Or in Edit mode press ctrl+alt+shift+m for non manifold edges and try to correct them.

Hope it helps

[CanRobo]

Thank you so much for the reply Kyriakos!

I will attempt to repair this as you suggested tonight and get back to you.

Thanks again!