Fix: You need to save the project keeping in mind that the relative path to the images should be valid. Like I had saved the project in some other directory, hoping Spine to magically update the internal file paths. It didn't.
Operating System: Mac OS X 10.8.2.
I was working on some animation earlier today. Was quite happy with Spine. But, at the next launch, all the images seem to be missing. The bones are animating fine.
Even the 'Set Parent' button seems to be disabled.
What am I doing wrong?