This is more of an FYI for the Symantec Techs. In the past, I (as well as other users) have had issues on one of my computers not automatically installing version updates in NIS 2009. See, for example:
http://community.norton.com/norton/board/message?board.id=nis_feedback&message.id=75187#M75187
I've been running NIS 2010 (NIS 17) ever since my failed update to version 16.7.
In case you are interested to know, my system successfully (and automatically) upgraded to 17.1 (from 17.0). So, something is different with at least this automatic update in NIS 2010 as compared to the past NIS 2009 updates. (And, if the folks at Symantec weren't following this problem, oh well -- I posted for nothing.)