Thanks for reaching out to us!
You should be able to load a 4000×3000 pixel image. There is a maximum supported upload size of 16 megapixels, however 4000×3000 falls within the allowed size.
One thing you can try: navigate to the Library > Get from Computer tab and try the Basic Uploader link (beneath the red Upload Photos button). This may work for you. If not, could you please email us an example image to support [at] ribbet.com so that we can investigate further?