Check your PC date and time first.
Right click the clock in the system tray. Select Adjust Date and Time.
Verify and correct the month, day, year, hour, minutes and time zone.
Reboot if you changed any of the above.
Information to help troubleshoot and resolve update problems -
http://social.microsoft.com/forums/en-US/onecareupdate/thread/9a6a0003-b91c-4518-966c-fc50450f0e41/
If none of that helps, please contact support.
How to reach support (FAQ) - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
-steve
~ Microsoft MVP Windows Live ~ Windows Live OneCare| Live Mesh|MS Security Essentials Forums Moderator ~