Depending on the type of geometry inside SolidWorks, it is possible that the STL file that is generated will be invalid. Try to make sure the part in SolidWorks is an actual 3D shape formed of a closed surface. You can try referring to the Solidorks Part file directly from the File Solid block. Another option is to use an open source geometry tool such as Blender or MeshLab to fix the STL. If you post the files we can take a look at them.