Looks like Qimage is telling you that you have unsupported formatted images in the folder.
I cannot tell you which and why, but perhaps the Mac is nutzing up the files, or some other intermediate software that you use is saving its files in some proprietary format.
If you were to make a NEW FOLDER and transfer all the images three at a time perhaps, to the new folder, and open Qimage looking at the them 3 at a time, and keep doing that until you get that error message from opening the New Folder, you could isolate one or all bad formatted images.
Email one to me...
wathree.ssz@verizon.net and then we can see why it wont open.
Fred