I'll be interested to see how this is resolved as I'm having the exact same issue. (Although I have no special anti-hotlink plugins installed.) Everything was working fine until a few days ago. Now, whenever I try to upload an image, I get an error message. I can see the individual image file name when I look in my Media Library. And when I click on the file name I can see my photograph clear as day. But I see this message when I click on EDIT IMAGE:
Image data does not exist. Please re-upload the image.
(I've also been unsuccessful in trying to create a simple gallery).
Thanks in advance for any guidance anyone can offer.