I also noticed that the parts in "spider-open-v1" are not quite the same as the STL models: the former have sharp edges while the latter have round ones.
Anyhow, those errors I mentioned before appeared when using the slicer "Simplify3D-v3.0".
Today, I started using the slicer "CuraEngine.exe" and the errors where ignored or vanished!
(which of them is the case, I don't really care!)
The parts are being printed as we speak and I believe I'll be able to get them all ready for tomorrow's assembly task!
Great job, regishsu !
And thanks for sharing !