cannot change network sharing settings

[Eduard Hoenkamp]

On one of my computers I cannot change the network settings. (Yes, 
administrative privileges, settings unlocked.) I want to allow remote 
login, but the option remains grayed out. If I start sshd manually 
(on the command line), then it lets me change that option, after 
which I can remotely log in, but the setting does not persist over a 
restart. I already fiddled with /etc/hostconfig and 
/Library/Preferences/com.apple.sharing.firewall.plist, but to no 
avail.
Anyone in the know? Eduard.