Some users have reported an issue wherein, after applying Security Update 2008-006 for Mac OS X 10.4.11, their systems repeatedly display the message "Your network settings have been changed by another application." This message is sometimes accompanied by dropous in wireless connectivity.
The potential fix is as follows:
Delete the following files from Library/Preferences/SystemConfiguration
This fix is similar to one that we've recommended for wireless connectivity issues after various security and system updates. It's a good first line of attack if you're having such problems after an incremenal Mac OS X or security update.