No luck, I haven't had a chance to dig into that section of code yet but on the demo site I did notice that under the Images-> Medium and Images -> Large directories you have a Product_with_attributes directory. I believe I have a duplicate directory structure to your demo after playing around with (and messing it up! I sent you 10 bucks for your trouble when I downloaded 3.1 btw :) )
Anyway is there any required directory structure under the images directory? Where is the Image Swapper writing the resized files to? And if the casing needs to be uniform could it be a problem if its attempting to append _MED or _LRG to the image file name? Maybe I'll try an uppercase file name and see if that works...
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