I've moved your post to the Secure WifFi topic folder, though I'm not quite sure that I understand the problem.
Are your referring to Windows Live OneCare?
Did you secure the wireless network using the option in OneCare when prompted that your network was not secure?
Are you only experiencing this from one PC? What is the *exact* message that you are getting? Does the error or message dialog have a title to it?
Cannot log on to what?