Why would an “command not recognized” error occur only when a window is populated?

Question

My record sheet app has a menu option for creating a new, blank record sheet. When I open a sheet window, I can open new windows without a problem, using subprocess.Popen() to d

Answer 1

The suggested answer seems to have fixed the problem. I also realized that I needed to use os.name to determine which OS is being used, then I can use the correct path format for loading the external Python file.