Ok, I am using Blender 2.7 on Ubuntu 14.04 LTS with 64 bit OS.
Objective: create a hollow cube with a hole as an exercise in using Blender to create files that can be 3D printed.
Steps employed (according to the tutorial):
-Set scene units to metric (and set the scale to 0.001)
-Scale by a factor of 10 (cube is now 2cm x 2cm x 2cm)
-Apply the scale
-Create cylinder mesh
-Scale it to appropriate size (to use to create a hole) and locate it just beneath cube
-Select cube, and in wireframe view, duplicate it and then scale so that it now forms the inside of the hollow cube
-Move the cylinder vertically through both surfaces of the hollow cube.
-Reselect the cube (presumably the outside cube surface?)
-Go to modifiers, select add modifier and select boolean
-Select the cylinder as the object and difference as the operation and click apply
-Move the cylinder down again (and can be deleted).
This is the point where what I get starts to differ from the results in the tutorial. I have uploaded the file created from this as: ‘cube test for Blender Artists 9-7-14’
In the tutorial the tutor proceeds to delete the protruding vertices leaving two holes: one in the inner cube surface and one in the outer cube surface. Then he looks for non-manifold vertices and bridges across the holes to create a ‘watertight’ object that is ok to 3D print.
I hope that is enough info and thanks!