I just ran into a 10.4.11 bug. If I get a chance I'll see if it's fixed in 10.5.
If a regular user locks a file in a shared folder, an admin user cannot unlock it and they cannot change ownership or privileges. The file is inaccessible.
The useless error message is: "The operation could not completed. An unexpected error occurred (error code 120)."
You have to log in as the regular user, click get info on the file and uncheck the locked attribute. Then you can change permissions.
It's easy to see how this bug happened. The "Locked" attribute goes back to Mac Classic 6 -- if not earlier. So this is a collision between a very old access control mechanism and OS X privileges.
I wonder if even "root" can take control of this file.
The error message suggests Apple missed this one. I wonder if it was fixed in 10.5 ...