I recently upgraded the copy of Norton Antivirus on my system from 2006 to 2009, but this weekend I had to uninstall 2009 and re-install 2006.
The reason for this was that installing 2009 had stopped a game from running (Sam and Max Season One DVD version). This game uses "Securom" for copy protection and the problem was that the Securom software displays a message complaining that it cannot find the DVD, even though it is in the drive.
Searching for the cause of this problem showed that Securom recommend uninstalling DVD writing software and disabling DLA as possible solutions to allow the game to run. This suggests that the Securom software is dodgy at best.
However, the game had run fine with NAV 2006 - what I don't know is if this is yet another problem with NAV 2009, or if this change is purely because Securom recognised NAV 2006 so allows the game to run, but does not recognise NAV 2009.
We are still waiting for you to fix the hotkey problems since that is also causing us problems - if that is not fixed then we may have to go elsewhere for antivirus software for our systems.
For now I have "worked round" the problem with my game by re-installing NAV 2006.
Incidentally, a secondary problem was that the uninstall of NAV 2009 asked why I was uninstalling it, but the web link I was asked to click on to give a reason failed...