Searching the forums yielded no clues to my particular problem I thought I'd post my findings for others.

Problem:

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. 

Solution:

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.