RL exercise 3 can not hit the policy server

[vahid-g]

In this first part of the tutorial, after implementing run_one_episode, client.start_episode() throws an exception:
ERROR policy_client.py:115 -- Request failed.
...

The system returned: (101) Network is unreachable

The remote host or network may be down. Please try the request again.

...

I checked localhost:8900 through my web browser and its up. I was wondering if there is a bug or am I missing a point?

Sorry if this is not the best place to ask such a question. I just didn't find a better place.