To correct:
The STL file 'package://wsg_50_simulation/meshes/WSG-FMF.stl' is malformed. It starts with the word 'solid', indicating that it's an ASCII STL file, but it does not contain the word 'endsolid' soit is either a malformed ASCII STL file or it is actually a binary STL file. Trying to interpret it as a binary STL file instead.
When launching Rviz with a URDF containing SolidWorks created meshes in STL.
Just go to the folder with STL's with this problem and do: