What's the reason behind making nginx a proxy server in this case?
Anyway it seems to me that the IP/port where you're forwarding the requests to is not valid or not reachable.
Traffic filtering.
How can it not be valid for posting threads but valid for everything else?
--------------- Added [DATE]1429820747[/DATE] at [TIME]1429820747[/TIME] ---------------
Also I just found out I can make small threads but not long threads without the timeout.