This could be a problem with an image that is saved with a PNG extension, which is actually NOT a png file (this often happens when you use "save as" on a PSD and name it with a .png, forgetting to actually convert the file).
So this is how I fixed it, I deleted all images and loaded them one by one until I found this one image, it was .png, but there was something wrong with it, so I did it again in Photoshop, and navel, the error is gone.