Are you using an app or device that won't work while McAfee Internet Security is running? This can happen when "ports" have been blocked or limited. You can open a port so the device or app can access the Internet.
Open a port
Open McAfee Internet Security.
Expand Web and Email Protection.
Click Ports and System Services.
Enter a program name, category, and description.
Enter the TCP or UDP port that you would like to open.
Change the drop-down option for Open Ports to All PCs.