When exporting a simulation of an assembly to inp-file, the resulting .inp-file contains all parts as one. All parts in the assembly gets the same part-id in the mesh in the exported inp-file. This is a problem.
(My project is offline and cannot be uploaded, but the question is quite general.)
1. create mesh (of all parts) in Solidworks Simulation.
2. Export to .inp-file: Simulation -> export
(as recommended by Jim Riddell in thread 185834 SolidWorks Simulation Mesh files export )