Getting error 504: Gateway Time-out in dev server - google-app-engine

Question

I've been struggling with a 504 error on my python app engine dev server.
I'm behind a corporate proxy but usually have no trouble by setting HTTP_PROXY and HTTPS_PROXY, I don't know if it is related to my problem.
In my code I use discovery from apiclient (main.py line 63)
driveService = discovery.build("drive", "v2", http=http)
When this executes, I get the following traceback
INFO 2013-10-07 13:49:42,812 discovery.py:190] URL being requested: https://www.googleapis.com/discovery/v1/apis/drive/v2/rest?userIp=%3A%3A1
ERROR 2013-10-07 13:49:55,848 wsgi.py:262]
Traceback (most recent call last):
File "C:\Program Files (x86)\Google\google_appengine\google\appengine\runtime\wsgi.py", line 239, in Handle
handler = _config_handle.add_wsgi_middleware(self._LoadHandler())
File "C:\Program Files (x86)\Google\google_appengine\google\appengine\runtime\wsgi.py", line 298, in _LoadHandler
handler, path, err = LoadObject(self._handler)
File "C:\Program Files (x86)\Google\google_appengine\google\appengine\runtime\wsgi.py", line 84, in LoadObject
obj = __import__(path[0])
File "c:\temp\iterlex-backend\main.py", line 63, in <module>
driveService = discovery.build("drive", "v2", http=http)
File "c:\temp\iterlex-backend\oauth2client\util.py", line 132, in positional_wrapper
return wrapped(*args, **kwargs)
File "c:\temp\iterlex-backend\apiclient\discovery.py", line 192, in build
resp, content = http.request(requested_url)
File "c:\temp\iterlex-backend\httplib2\__init__.py", line 1464, in request
cached_value = self.cache.get(cachekey)
File "C:\Program Files (x86)\Google\google_appengine\google\appengine\api\memcache\__init__.py", line 559, in get
results = rpc.get_result()
File "C:\Program Files (x86)\Google\google_appengine\google\appengine\api\apiproxy_stub_map.py", line 612, in get_result
return self.__get_result_hook(self)
File "C:\Program Files (x86)\Google\google_appengine\google\appengine\api\memcache\__init__.py", line 615, in __get_hook
rpc.check_success()
File "C:\Program Files (x86)\Google\google_appengine\google\appengine\api\apiproxy_stub_map.py", line 578, in check_success
self.__rpc.CheckSuccess()
File "C:\Program Files (x86)\Google\google_appengine\google\appengine\api\apiproxy_rpc.py", line 156, in _WaitImpl
self.request, self.response)
File "C:\Program Files (x86)\Google\google_appengine\google\appengine\ext\remote_api\remote_api_stub.py", line 200, in MakeSyncCall
self._MakeRealSyncCall(service, call, request, response)
File "C:\Program Files (x86)\Google\google_appengine\google\appengine\ext\remote_api\remote_api_stub.py", line 226, in _MakeRealSyncCall
encoded_response = self._server.Send(self._path, encoded_request)
File "C:\Program Files (x86)\Google\google_appengine\google\appengine\tools\appengine_rpc.py", line 393, in Send
f = self.opener.open(req)
File "C:\tools\Python27\lib\urllib2.py", line 397, in open
response = meth(req, response)
File "C:\tools\Python27\lib\urllib2.py", line 510, in http_response
'http', request, response, code, msg, hdrs)
File "C:\tools\Python27\lib\urllib2.py", line 435, in error
return self._call_chain(*args)
File "C:\tools\Python27\lib\urllib2.py", line 369, in _call_chain
result = func(*args)
File "C:\tools\Python27\lib\urllib2.py", line 518, in http_error_default
raise HTTPError(req.get_full_url(), code, msg, hdrs, fp)
HTTPError: HTTP Error 504: Gateway Time-out
HTTPError()
If I try the offending URL with curl in the same console windows, it works (i have to use the -k option though)
C:\temp> curl -k https://www.googleapis.com/discovery/v1/apis/drive/v2/rest?userIp=%3A%3A1
{
"kind": "discovery#restDescription",
"etag": "\"XflbyoTZtBo225MnsgwJQ-FHlhA/AFnpisGyT0XxOrZz7gMWdR5PpRg\"",
...
Being new to app engine and python, I confess I'm a bit lost, any help would be greatly appreciated
Thanks!
Nicolas