When NAV or Mcafee goes bad I usually uninstall it and start from scratch again. When I do this I usually follow the procedure below:
Go to run type "msconfig" then go to the services tab. Above the ok button you will hide all microsoft services put a check in there. The list will get smaller. Uncheck everything that belongs to Mcafee. Hit the apply button, close button, then restart. When you restart you will get a message that you have changed some settings place a check mark in the box that states dont show this message again. Uninstall Mcafee. Restart the machine. Make sure you have no traces of Mcafee and then reinstall Mcafee update your files and everything you should be ok.