What happen is I first uploaded 2 images as photo. And then after posting the topic. I went back in and tried to make a bigger thumbnail for the images I've already uploaded as photo by selecting insert > large. Then I will get this error message.
Also if a image is uploaded as photo there doesn't seem to be a way to delete it, by selecting edit photo and click on the remove icon doesn't seem to work. Have to delete the whole post in order to delete that photo?