This has been an ongoing issue with the OneCare firewall for years, unfortunately. The solution is to turn the firewall off and then on again, which usually resolves the problem.
Sadly, the solution is to stop using OneCare. Since OneCare is at end of life, it will not be updated and you will be unable to renew when you current subscription expires.
The replacement, Microsoft Security Essentials, which is free, enables the Windows Firewall and the problem should no longer occur.
See this post for End of Life information for Windows Live OneCare - http://social.microsoft.com/Forums/en-US/onecaregeneral/thread/81996436-edad-41ba-bdfc-02fc094e2ca9
-steve
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