Path Changed in Python Script Executed by Another Python Script

A script at /foo/bar.py tries to run a second script /main.py using the subprocess module. Although main.py runs fine with python main.py in the Windows command prompt, running bar.py which calls main.py causes an error

ConfigParser.NoSectionError: No section: 'user'

Why is there now a problem with the path to settings.ini, and how can we fix it?

~/settings.ini

[user]
id: helloworld

~/foo/bar.py

subprocess.Popen([sys.executable, "../main.py"])

~/main.py

Config = ConfigParser.ConfigParser()
Config.read("settings.ini")
userId = Config.get('user', 'id')