Can't get motion loads in cosmosxpress from an assembly

Hello,

    After running a physical simulation,andthen running cosmosxpress on a specific part in the assembly,anerror occurs every time.  It says "failure occurredincomputing part forces".
    Being a new user, I'm fairly certainI'mdoing something wrong, but I can't figure out what. Cananyoneoffer assistance.

Thanks.SolidworksSimulation