Can you expand a bit on what you mean by slide layer?
Objects on a slide can be layered in a sense but they are not something that can be navigated with the use of a go to previous slide button. That would literally take you to the previous slide in your project (obviously not meant for Slide 1) but it would not reveal something that was positioned underneath another object on the stage.
Can you provide a screenshot of what you have going on?
Captivate has no slide layers. Each object or group in Captivate appears as a separate timeline in the Timeline panel. No interactive object will you allow to move between the 'layer' timelines at all. Can you please insert a screenshot of the timeline with the Back button selected?
What is maybe closes to what you want is to have a multistate object, and move between the states in that object by using one of the three commands: