Dan: Thank you for taking the time personally addressing this issue. I restarted Stream, and used a steam://flushconfig command before restarting my system. The error message is still present following a file validation, but has now changed to .../Universe Sandbox x32.exe. I notice that in the directory has a folder called x32 containing the executable being called. Perhaps the launcher should be calling .../x32/Universe Sandbox x32.exe instead?
Cesare: At this stage, I tend to believe that the 64-bit is not only better but is essential for optimum performance. With the 32-bit version, if I have more than just a few stars active at one time, my computer initiates an emergency shutdown procedure in a matter of minutes due to overheating processors, even if I disable every graphics intensive component of the simulation that I can.