Searching the forums yielded no clues to my particular problem I thought I'd post my findings for others.
Clicking 'Run' provided a pop-up window telling me to 'define elastic modulus'.
All items in 'Parts' container had material properties defined locally in SW simulation.
Parts which were treated as remote masses appeared in the 'Remote Mass' container with the original '[SW]-6061' solidworks defined properties. Reapplying the properties locally in simulation to the items in the 'Remote Mass' container fixed the problem.