OK, you get a traceback telling you line whatever, prop not found, but when you look at that line, you can't seem to find any property there. If that line has anything beginning with a $, (as in $string_utils, $rpg, $player, etc), whatever has a $ in front of it is a reference to a property on #0 (aka The System Object). When something is "@corified" on a moo, a property is added to #0, so when you see something like $string_utils, that means that you can also find:
@show #0.string_utils #0.string_utils Owner: Wizard (#2) Permissions: rc Value: #20
So if you can't see an obvious property that is being referenced, see if the "prop" referred to is a corified object.