Not finding someone and not being able to add someone are two distinct issues.
For the first - not finding someone - that may not necessarily even be an error. If you say you are added two Cisco users - can I assume you are not from Cisco? In that case, you are adding external users who shouldn't come up during the predictive search anyway. Even if they don't come up, you should still be able to enter the email address and hit return.
For the second - not being able to add someone - I'd echo what Lukas asked - what type of error or behavior do you see when you try to do this?
Thanks Christopher and Lukas.
I am a Cisco user, unable to find (and add) two other Cisco users. Christopher's comment prompted me to enter the entire email address (including the @cisco) to add and that worked. It was not clear to me previously that would be possible as the other individuals I added were found with auto-complete. Anyhow, my issue is fixed.
Great! And since you're a Cisco user, feel free "Spark me" directly if you have any other questions since I'm internal too!