I’m no pro but I had the same issue a few days ago, and I think it was because I tried to upload pics from other website. I had to screen shot it before sending it again and it worked. Maybe that will work for you, if your problem has the same origin of c...
Thanks for the suggestion. I actually sent a photo I took with my I phone and sent it to my IPad. I am going to send the same photo at a lower resolution to see if that works .