Go to your system clock in the lower right-hand corner of your screen and double-check that it is accurate for both the time and time zone.
Try these two FAQ's to see if they help:
The detection signature file is between 8 and 29 days oldand
McAfee applications are not able to update through authenticating Proxy servers causing Signature fi...If these don't help then we need more information....
Please include the following information: What is your operating system, service pack and are you up to date with Microsoft update? There are two ways of checking this. Go to Start/Run and type in winver then click the Enter key. Or, right-click My Computer in the Start Menu or on your desktop (or Computer in Vista) and select Properties.
Post what it says. Also post what browser and version (from Help/About) you are using and how you connect to the internet.
What McAfee products do you have? If your taskbar icon is like this:

- right-click it and go to each application "About" and post the details.
If it is like this:

- double-click to open SecurityCenter and then click "View Details" or "About" at the lower right of the new window. Post the details from each module.