NAV will not install protections but no error message?

I am running NAV 2011 version 18.6.0.29 in XP.  Recently, NAV warned that I was "at risk" but when I hit "fix now" it runs Liveupdate and appears to install everything but then shows "protections not installed".  No error message.  In fact, One Click says there are no problems but I continue to get "at risk" warnings.  What is up??