McAfee apparently had a bad update go out last weekend -- reports in their forum vary from apparently systems that won't run to loss of Internet access to blank McAfee app windows & missing script errors. I was lucky & just had the blank windows for some stuff & script errors when I tried to change firewall settings -- I wasn't aware of any problems prior to trying to change those firewall settings this evening. I also couldn't get McAfee to update, so I suspect it hadn't updated itself since last weekend. I was able to get it to update finding & running C:\Program Files\McAfee\MSC\mcupdmgr.exe in Windows' Explorer. After a restart that *might* have fixed the problem, but I also ran a McAfee Virtual Tech app before re-booting that added 2 registry entries -- I don't think they would do [or did] anything but I could be wrong.
Trying to find out what was happening a page on McAfee's site directed me here: http://service.mcafee.com/faq/TS101446.htm
That's where they describe fixes & link to the Virtual Tech app.