It's been an intermittent problem for about a month now and I find that simply right-clicking the taskbar network icon which you can enable next to your system clock and selecting 'Diagnose and Repair' does the trick in a few seconds. They are still not sure it is a McAfee issue and not something to do with a Windows update not behaving well with the software, but are investigating. A fix isn't usually announced but just comes in silently and may or may not require a reboot to take effect.
There have been a number of threads about this and variations on a similar theme.
Sorry for the inconvenience.