Trying to use Boolean (difference) Modifier on a ring design and its not working correctly? Okay so I followed this  you tube video to make this ring and they way it is done on the video isn't working for me, I am not sure what the problem is. I have tried everything I found on the internet,!
advice from author 

activating the 3D print tool addon and running the  solid to check for problems, 
which it is saying I have some non manifold edges,!
 which are there bc those sides do not have faces because I used a mirror modifier on x and y to complete my basic shape, but I don't know how that could be the problem with the boolean because that is how its done on the video and it works??  I have done everything i can think of, even rearranging the modifiers,results from the video 
I have checked all the normals 
I'm out of things to try, please help?
Boolean operations sometimes fail when vertices between the two objects line up exactly.
You can work around this by moving one of the objects a very small amount.

Example .blend

Also see “Cannot execute boolean operation” when subtracting several spheres and cylinders from cube