This might be super easy to resolve...or not very easy to resolve.
Easy try first.....Select "Separate Connected Surfaces" from the Mesh menu. If the model list jumps from one (or whatever is is) to at least one more, then try slicing again. Seach the forum if you're wanting to know what this is all about.
Not so easy.....your model may have been generated with too thin walls....resulting in S3D not printing something it can't print correctly. Invoking single extrusion walls and playing with the associated settings might help.....otherwise the model needs to be designed with thicker walls.
From what I can see, my money's on option one!!
EDIT...having taken a closer look....definitely option one....