If this is the same cutlist plugin cited in the above post by Jeff Hammond then what you need to do is make all your geometry into either a group or component before you run the plugin. My personal preference is to make things into components, I rarely use groups and then only temporarily until it is made into a component. So if you are making a simple rectangular box with an identical top and bottom, sides and front/back you will have 3 components. One component will consist of the top and bottom, the second component will consist of the two sides and the third component will consist of the front and back. For this plugin to work everthing should be either a component or group (ideally a component with an identifying name). If there is geometry that is not one of these the plugin will not give a useful cutlist. I suspect that in your situation, none of your geometry has been made into either a component or group and that is why you are getting the error message. Hopefully this helps.
John