Is the Windows Firewall blocking printer sharing and causing Error 709?

Yes, the Windows Firewall can block printer sharing. Ensure 'File and Printer Sharing' is enabled in the Windows Firewall settings. Go to 'Windows Security' -> 'Firewall & network protection' -> 'Allow an app through firewall'. Look for 'File and Printer Sharing' and ensure it's checked for both Private and Public networks (though Public should be carefully considered for security).