I'm not sure what you mean by that.
Can you run lsynth on the command line?
"C:\Program Files (x86)\LDraw\LSynth\lsynthcp.exe" "c:\somewhere\myfile.ldr"
Can you run lsynth on the command line?
"C:\Program Files (x86)\LDraw\LSynth\lsynthcp.exe" "c:\somewhere\myfile.ldr"