How do I join the output meshes of the Cell Fracture addon? I have a simple, unsubdivided plane mesh with a particle system that I want to apply Cell Fracture on, following this step-by-step guide: http://blendersushi.blogspot.de/2012/07/vfx-voronoi-cage.html

But I'm stuck at the part where the author writes


  For the purpose of creating Voronoi Cage, I actually just need the "wireframe edges", so I join the Shards back into a single mesh (CTRL+J).


, since there is nothing to join.

Here's a screenshot of my Cell Fracture settings:


And here's what Blender looks like after applying Cell Fracture:


Selecting the original mesh named "Plane" and hitting Ctrl+J yields "No mesh data to join", while selecting any of the new "Plane_cell*" meshes and hitting Ctrl+J does nothing, not even displaying some error message.

I'm certain that I'm missing something crucial, but I can't figure out what.

(Sorry for the uninspired tag choices, no other tags looked appropriate.)
Your fractured objects are on the second layer. The original object is kept unmodified on the first layer. 

The following is a good, detailed video tutorial on the subject: https://www.youtube.com/watch?v=GTq9sLQOiVs