[warn] Received http status code 404 ("Not found") from server 'x.x.x.x:9001' while fetching "/tor/keys/fp/(40-key-characters and numbers)".
Is there a way to allow the keys? Is it important to have the keys for that session?
The error means you got a 404 - not found while asking a directory cache for the key certificate for the authority identified by the fingerprint <40-key-characters and numbers>. The address x.x.x.x is the cache itself.
Tor will try another for you.
-- leeroy