Try  system('J:\VSS\win32\ss.exe','cp',"$/Some/Thing");

Your single-quotes in  system('"J:\VSS\win32\ss.exe" cp "$/Some/Thing"'); cause the double quotes not to interpolate. So you are running the command
C:\>"J:\VSS\win32\ss.exe" cp "$/Some/Thing";.

HTH

grep

grep> cd pub grep> more beer [download]