Triggers not working

I'm building a course on Alcohol Awareness. Part of the course consists of a graphic of the human body with callouts that open a new layer giving information on the effects to that organ etc. The user can then click on the layer or a button and return to the graphic ;layer.

In total there are about 11 callouts leading to 16 layers (some layers have supplementary layers). This started off well enough and for the first 7 or so I had no problems. In the later ones, even though I carried out the same procedure the trigger to return to the graphic does not work in these layers. I have deleted the layers and started again - same result.

Are there limitations in Articulate Storyline to the number of triggers or layers that a slide can have. Or, since I am still on a 30 day trial of the software, are there limitations on the functionality of the trial version?

Thanks for your help

John