I remember having this error too, if I remember right it is because of small differences between the two sketches, like if the origin of the circles does not coincide exactly or the "shell circles" have not exactly the same diameter. It would create extremely thin pieces, and it's why it tells you it can't create the bodies
I've checked the sketch tens of times over and all of the circles and line segments are correct. Another thing that I noticed is that the split works up to the third shell; the first 2 shells always build correctly but the third one is causing the issue somewhere.
EDIT: I adjusted the cut depths to be equidistant from the origin in the third shell, and now it works correctly...but unfortunately, I need the cuts to be at a very specific depth in the third shell, and that requires them to be at different distances from the origin. My question is, should it work even if I do this?
DOUBLE EDIT: After readjusting the sketch to where I needed it after the split, it still didn't work. So, I tried something else. I approximated the cut depth by a thousandth of a degree to where it was supposed to be, and IT WORKED! The cut depth isn't exactly where it needs to be to eliminate certain pieces, but it is so close to it that those infinitesimally small pieces can be omitted.
Sorry for wasting your time everyone...