I know what it is: the 3rd word in the game is "LAS", and "CLASSEES" goes through that path.
From these rules: http://www.wyps.info/other/oski/
"A new word cannot contains some used word. For example if was played word MAN, is not possible to play MANY or HUMAN."
And this example also falls under:
"Used words cannot contain a new word. For example if was played word KEYED, is not possible to play KEY or EYE."
Good luck! ;)
JY.
Another thing that might not immediately be clear is that while jytou played CALE as the first move, there is actually a zero-th move which is the default 3-letter word appearing at the very beginning of the game. In this case this word is LAC and it follows that you can't make any word that incorporates it.