I got the same error, I checked the type of images that I got downloaded from the internet, so before that I was naming my images, for example,cat.0.jpgcat.1.jpg......cat.100.jpgHowever, After getting the error, I read the info of some images, I found all images are jpg types from the original source, for example,https://cdn.pixabay.com/photo/2016/09/13/05/47/gears-1666494__340.jpgAnd I found five images were png types, like this:https://cdn.pixabay.com/photo/2017/08/19/23/54/email-sign-2660276__340.pngSo, I changed these to,cat.55.pngcat.34.pngAnd jumped to the create ML againg hitting the start training button, it runs correctly, but I realized that these 5 images of type png are not recognizable from create ML at all so replace with other data of type jpg.Hope this helps anyone will have the same error!