I ran into a problem using Spine with Photoshop's export to layers script. The script adds numbers to the file-names which can change when you add any layers to your model which means Spline can't find them. Rather than rename each individual layer I discovered you can easily edit the "export to layers to files" script to not add the extra stuff to the file-name.

http://graphicdesign.stackexchange.com/questions/10669/cs5-export-layers-as-files-no-number-sequence

You have to use unique names for each of your layers else they will get overwritten.