Double check that all bodies in each part have a material applied in the simulation.
You may have also selected a material from the library that doesn't have an Elastic Modulus defined like woods, rubbers and carbon fibers.
The only way I could get the error to go away was to manually assign each part's material from the simulation tree "parts" section. I just re-assigned all the same materials that I have defined in each part itself in Solidworks.
None of my parts had multiple bodies or surfaces, just one.
I'm not sure what changed, but that seemed to work.