Hello, I have a Win XP and a Win 7 Pro 64-bit networked via router and ethernet cables. At this very moment, from my XP computer I can open files that reside on the Win 7 hard drive, which tells me that the ethernet connections work. But about half the time, the Win 7 cannot connect to the Internet, giving me an error window "Error connecting to broadband connection" and inside the window is "Cannot connect to phonebook entry" Rebooting the Win 7 computer does not resolve the problem. Same error window.
My guess is that you have a dial-up (RJ-11) port on your computer that you aren't using. Try disabling it (in Windows Device Manager, or better yet your PC's BIOS).
I think that this problem could be caused by having incorrect settings in the connections tab in Internet Explorer, options.