Ok, now... how many bottom, side, and top layers? What is the percentage of infill? What is the Extruder temperature? If you can give us this info, it'll be a lot easier to help.

I'm betting that your infill is way too low, but... those layers mean a lot also. On S3d, for any of these parameters, select "Edit Process Settings". From there, infill is the slider bar. To increase layers, select "Layer", they're all right there. Of course there is always the possibility that you have your extruder temp way off as well.