Make sure you've converted everything to paths and that you don't have groups that need to be ungrouped first. You can look in the status bar on the bottom of the screen to see if everything you've selected is a path. It will say something like: 4 objects of type path. Or: 4 objects of type path, group, rectangle.

Ok thanks, i have figured it out now, the tutorial does not list everything needed as it says nothing about combining the shapes after the subtraction stage to get a solid shape. Thanks