If you are running Windows XP, you might be running XP's built-in Internet Connection Firewall (ICF) without your knowledge, since it is the default. Follow these steps to ensure that the correct ports are opened.

1. Click "Start," "Settings," and select "Control Panel."
2. Double-click the "Network Connections" icon.
3. Right-click the connection that you use to connect to the Internet, and then click "Properties."
4. On the "Advanced" tab, uncheck the "Protect my computer" checkbox if you want to disable the firewall. If you only want to open the webcam ports, check the box and continue with the remaining steps.
5. Click the "Settings" button.
6. Click the "Add" button.
7. Under "Description" fill in Yahoo! Webcam. Under "Name or IP" fill in 127.0.0.1. Under both "External Port" and "Internal Port" fill in 5100. Check the "TCP" button.
8. Click "OK" to close all opened dialogue boxes.