Some times you'll see a message telling you that Ariv doesn't know this. Remember that Ariv only has access to information and conversation threads that you gave it access to so unless that bit of information exists in those threads she won't be able to find a relevant response for you.

Asking the question differently could yield a result in the event that the AI engine did not decipher the intent correctly. Do try more than once, and give Ariv a chance to learn.