Why might Joe be having trouble accessing shares on his home media server while connected to the Internet?

Joe may be having trouble accessing shares on his home media server while connected to the Internet because a firewall could be blocking the required ports for the sharing protocol. Media servers often use specific ports to allow access for clients; if the firewall settings do not permit inbound or outbound traffic on these ports, access will be denied.

When a firewall is enabled, it can prevent network traffic that is not explicitly allowed, which includes local network shares. Consequently, to successfully connect to the home media server, Joe would need to configure his firewall to create an exception for the media sharing service, ensuring that the relevant traffic can pass through unimpeded.

While other factors, such as an IP conflict, a corporate VPN, or HomeGroup settings, can impact network connectivity, the most immediate and relevant concern for accessing shared media files, particularly when connected to the Internet, is ensuring that the firewall is not obstructing the necessary communication.