What does "The operation could not be completed because an error occurred when creating frame 0 (error -1)." mean, and why does it keep happening?

I ended up figuring out a solution, but I'll get to that in a sec.

To answer your question, I converted the .wmv file in a program called Media Converter (available in the App store), and converted it to an h.264 file (then later to a .mov file, and then to an .mpg). I could view the file, and work with it in projects, but any project I tried to output with any version of said file, would result in the afor mentioned message, with the same results in FCPX (and Compressor 4 as well). I tried multiple frame rates, resolutions, files types, re-converting the file, all with no luck. My impression from said experiments, and reading other discussions was that it was a corrupt file.

Then I got frisky...and a little desperate. I brought the converted file (the .wmv to .mov) into Motion 4... and an export worked first try. So I exported a pro-res file from Motion 4, and used that file in the already built Motion 5 project, and voila!

So, who knows what that means in real terms, as for the whats and whys.