I don't think that's the problem since each time I try it's on a new VM.
Not too sure what you mean by unblock but if I understand correctly it would work to open images included with the tool, resize image , import PNG, merge and hit save in PS. I will try without altering the images next though so we can know for sure if it is the images causing the problem.
make sure the images are the same size as the default images, also you can add those images to the shell32.dll.mui file, first create a res file from the shell32.dll with those 2 images and then add that res file to the shell32.dll.mui file, then replace the images after with your custom ones, restart to take effect.
This also has the added benefit of not needing to replace any signatures and it's also allot safer, it should boot no matter what.