The 'Set Builder' software is fairly basic in its design so there are few things that can go wrong.

It is important that you resize your images before putting them into the Set Builder.  Whilst the Set Builder will resize them for you it is a slow process and if the image you are processing is large it might take a little while for it to complete the resizing.  So, wait a bit longer to see if it comes back.

You know that an image has been added to a Reel when the image appears as a thumbnail at the bottom of the window.  If it doesn't appear then make sure that the image you are trying to use is a valid bitmap or jpeg.

Before a Reel can be completed you must add 8 individual small images and 1 big picture.