I did miss a few things in my description of what to do, so this is the most likely problem. First, every object needs to have a name in Spriter, (double click a sprite or bone in persistent object palette, or bone hierarchy view to rename) the next release of Spriter will give default names even if you don't name them, but in the meantime that's the most likely problem. Also this early version c2 plugin doesn't yet work with bones, or nonpersistent(untweened) objects.
However, I have to recommend you not to bother with this version at this point. Just got another email from Ashley, and he's made quick progress, and the automatic version of the plugin should be coming soon. Also, I'll most likely add bones before then as well.
Sorry for the inconvenience.