As you can see the thumbnail for the album is fine just the images inside. If it is of any use this page was already created as an ImageGalleryPage page type that I just changed to the SlideshowProPage page type.
I Created a new SlideshowProPage at http://supportact.com.au/ss/new-slideshowpropage/ but the xml still does not have the tn and src values for the img tag. For some reason $Thumbnail.URL and $Large.URL does not return a value in the GalleryItems control.
Not that I have a real clue, but when looking at the template for an ImageGalleryPage I can see that $ThumbnailURL and $ViewLink were used. I even tried these in the xml template but that didn't make a difference.