Vista not recognising McAfee

Hi,

I am getting a message from Windows Security Centre that tells me
'Windows did not find antivirus software on the computer'.


But I have McAffee installed which tells me that I am protected
(everything is on). This programme was installed when I bought the pc,
updates automatically, and has never caused a problem before.


Can anyone tell me how to get Vista to re-recognise my antivirus
programme


Thanks

Ps I have scanned the hard-drive. It is clean.