If the security center doesnt receive all the updates , thats the time you will get an error as mentioned. It might be caused to due many reasons like, some other antivirus (might be remnants) blocking the updates, due to internet connectivity. . .
Please follow these steps to update to virus definitions:
1.Check the system clock
2.Check and delete if you have any other antivirus software in control panel or C:/progrma files/common files
3.Run virtual technician from http://mvt.mcafee.com so that it auto updates the virus definitions DAT files.