Hello Caroline. From your description of the problem it would seem like the upload process is timing out. This can happen depending on how many images you are trying to upload at the same time and the speed of your internet connection. Please try uploading images one by one. Pick one image, then click save, then pick the next, click save, and so on, see if that fixes the problem. If it does you can also try uploading 2-3 images at a time.