When I add new photos to a portfolio, the new image is added but it also displaces an image already in the portfolio. An example is here. If you look at the third image in the top row and enlarge the view you will see that a different image is in place. http://fergalmcgrathphotography.com/index.php/photo-gallery/products-albums/
Thats interesting. Did you by accident use the same names on those images? I believe you did.
anyway goto the striking advanced settings and enable clear cache.
browse your media library and give each image a unique name. They cannot be the same due to the striking caching system. make sure you uplaod each image under a unique name. !!
Ok, I went through a bunch of images and renamed them and they uploaded without any problems. I was chatting to the client and he said that he batch processes his images in photoshop and never changes the file names, so pretty much that was the problem.