Sometimes, Windows Security Center stop recognizing your antivirus or firewall... The fix could be fairly easy for the most part.
1. Go to control panel and open Administrative tools.
2. Click on services.
3. Go down to Windows Managament Instrumentation.
4. Stop this service. Stop Security Center service too.
Let them to Automatically start.
5. Exit out of this area to your desktop.
6. Right click Start and choose Explore.
7. Go to c:\windows\system32\wbem\repository.
Delete this subdirectory
ONLY. Let the others there.
Sometimes, only using
Unlocker,
MoveOnBoot or
Delete FXP you can delete these files.
8. Exit back to your desktop and reboot your computer (maybe you need to boot twice).
This will rebuild the deleted folder and the database. Once restarted, Windows Security Center should show the correct info and antivirus and firewall should now be recoginized

Other answers for XP Security Center not detecting antivirus or firewall program could be found here:
http://support.microsoft.com/kb/883792.
On Vista, the following procedure seems to work:
1. Go to control panel and open Administrative tools.
2. Click on services.
3. Stop these services:
Windows Security Center
Windows Managament Instrumentation
SBSD Security Center Service (if you use Spybot Search & Destroy).
4. Let all them to Automatically start.
5. Remove the directory C:\Windows\System32\wbem\Repository
6. Go to Services and Continue all the Services above or go to next step.
7. Reboot
Or, create a .bat file with the following content:
echo off
cls
echo.
echo Stopping Windows Management Service - please wait ...
net stop winmgmt
echo.
echo.
echo Removing Repository folder - please wait ...
rd /S /Q %systemroot%\system32\wbem\Repository
echo.
echo.
echo Starting Windows Management Service - please wait ...
net start winmgmt
cls
echo.
echo Done!
Run it in Vista as Administrator (right click the file and chose to run as Administrator).