Reader Mike Williams appears to be under fire from his Mac’s firewall. He writes:
On my Dual G5 PPC with 10.4.11, when I go to System Preferences -> Sharing -> Firewall it says “Firewall is off” and the options are grayed out because locked. When I unlock them with my Admin password, I get a drop-down that says “Other firewall software is running on your computer. To change the Apple firewall settings turn off the other firewall software.” I have no idea what the “other firewall software” is.
It’s quite likely that unless you’ve installed a firewall application in the past and have since forgotten you've done so, there is no other firewall software. Rather, your Mac is confused. In such cases the first thing to try is restarting your Mac.
No go? Okay, then let’s clear the firewall settings.
To do so, launch Terminal (found in /Applications/Utilities) and enter this command, which flushes your firewall settings:
sudo /sbin/ipfw flush
You’ll be prompted for your password. Enter it and confirm with a Y that you really do want to flush the settings.
Now enter this command to reload the firewall settings from the firewall’s preferences:
You should now be able to use the firewall within the Sharing system preference.