Could you take a screenshot of what you tried to enter? It's likely just a syntax issue with the entered text.
4 years ago(+1)
I'm having the exact same issue :( I typed "Is" exactly as Laguna said and it says "Invalid Directory. Application Not Found in This User's Directory."
I got much further than I initially expected (the first problem resolved itself; I forgot the period before a command line), but I have another, related, issue with the terminal. I'm having a hard time figuring out the admin password. The above command is registering as an error. I also searched the 'other' folder, but the cryptic message didn't help me out much. Now that I've passed the learning curve, I actually find the terminal mechanic to be extremely clever, fun, and (mostly) intuitive. I'm just bad at cryptic puzzles which is dampening my progress.