system
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I had an issue with the Windows Security Centre too.I did follow some of the solutions provided namely resetting the winmgmt service in the command prompt. I rebooted and nothing had changed. The security centre still wasn’t detecting that Avast! was up and running. I then tried disabling shields for ten minutes and security center detected that. It decided that Avast! was “snoozing” and asked me if I wanted it turned on which I did of course and problem solved. 
Unfortunately I have only just done this so I don’t know if it’s a long term solution.
I’m on vista ultimate on a lenovo T61p. avast version 2014.9.0.2006