I cannot click the option under the Layers menu in order to invoke the plugin. The image I'm working with is a single-layer pre-existing PNG. I've selected the only layer (Background) but the option is still greyed out. I've also tried creating a new layer and copying the contents of the background layer to it, but selecting that new layer still doesn't help.
I'm using GIMP verison 2.6.11 on Windows 7 64-bit (the program is 32-bit). Thank you for your help!