Does it provide any clues or text as to why you cannot modify the rule? Are all the options grayed out?
I suggest logging out then logging back into the console then try again, or try from another machine. If that doesn't work, verify that the LEM username has the correct role.
Admin user is being used.
Options are grayed out.
Log out did not help.
Reboot did not resolve.
Tried moving it to another folder (Custom Rules) and no change.
No other error except that you can't do it.