This can happen for various reasons, hard drive reading errors, OS or even McAfee corruption etc.
The first thing to try would be the Virtual Technician to see if it can find and fix issues: http://mvt.mcafee.com/
What operating system and service pack is this and what version of Internet Explorer is installed, regardless of which browser you use?
I use Google Chrome
Regardless of that, I repeat, what operating system and service pack is this and what version of Internet Explorer is installed.
McAfee and many other processes use Internet Explorer despite your browser defaults.
I am using windows 7, internet explorer?, Service pack?
Right-click Computer on your desktop or in your Start Menu and then Properties, it will tell you there if service pack 1 is installed.
Open Internet Explorer and go to Help/About, it will tell you there what version it is.
Sevice pack 1 is instralled and internet explore 9.
Good, thank you. Make sure that Windows is up to date including updates for IE. Windows Update should be offering IE10 so I would accept that as it's more secure or go HERE to download it, but before you do all that there are few things to try assuming you tried the MVT I mentioned in my first reply.
If not, run it first - http://mvt.mcafee.com/ and run it again if it says it can't fix something.
Run a disk check (using the /r parameter if Option 2 is used in the following link) to repair disk read errors. Here's a Tutorial on how to do it: http://www.sevenforums.com/tutorials/433-disk-check.html (Note: this can take quite a long time especially on large drives).
If that doesn't help try the uninstall, cleanup, reboot and reinstall as outlined here: http://service.mcafee.com/FAQDocument.aspx?lc=1033&id=TS101331
If all that fails to help I suggest you contact Technical Support via the link under Useful Links at the top of this page. It's free by phone or online chat.