Hi,
Please clarify/follow the below steps.
1. What is the operating system? Is it Windows Xpnull or Vista?
2. Open Mcafee Security Center & check what is the exact message that is displayed on the right pane of computer & files & Internet & Network.
3. Check the system date & time.
4. Check for older version of Mcafee i.e.(if you have any other Mcafee program except Mcafee security center),If found remove the same.
5. Check for other security software, have detailed information of other security software go to the link
http://service.mcafee.com/faqdocument.aspx?id=TS100376&lang=en_US&prior_tid=2&AnswerID=16777217 & remove if anything found. Restart the computer & then try to update.