Ah I took a look at the file on clough42's thingiverse
http://www.thingiverse.com/thing:335613 and I think I see the problem. If this picture you posted above is the complete result of the print, you need to flip it over and try printing it again. If you look at rendering of his model for this part, this is the orientation you want to print it in. The part missing from your print was printed without support and fell through/failed (which is why it's designed to print as pictured, then you won't need support and it should come out just fine).
Also one hint for slic3r that is extremely useful. You may know this already and if so I apologize. If you double click on the part you placed on the simulated bed in slic3r, you get a very nice 3d rendering of the part which is really useful to make sure everything is oriented the way you wanted!
Good luck!