keynote transition issue

I am having a problem setting up a new presentation. I want all the slides to transition on one click of the mouse using "disolve". This works fine of some of the slides but on others when I click to advance the slide the image goes to a black background and then requires another click to show the new slide.

The Transition settings look identical and I cannot work out why different slides behave differently. What do I need to change in the settings to make it transition smoothly from one slide to another?

Hope someone can help with some clear advice because this is infuriating.

Nick