Just wanted to share my experience – we had an image that was taken as a photo on a phone.
It wasn’t large – under 300K but when I pulled it up in Photoshop Elements, it was 28 inches across.
So I resized to 4 inches and saved for the web. All worked well then. Just in case it would help anyone else. I found this problem because it was just this particular file that was giving us problems – not EVERY image we tried to upload.
Good luck!