I'm also running into this error message when attempting to map out relationship between portal items, in this case a web map and a layers in the map.
zoningItem.related_items('Map2FeatureCollection', 'forward')
returns an empty array
While running the dependent_upon or dependent_to methods returns:
Unable to get dependencies for item: item
Unable to retrieve item dependencies.
---------------------------------------------------------------------------
RuntimeError Traceback (most recent call last)
<ipython-input-3-2b1d726173d1> in <module>()
----> 1 zoningItem.dependent_upon()
/opt/conda/lib/python3.5/site-packages/arcgis/gis.py in dependent_upon(self)
2993 def dependent_upon(self):
2994 """ Returns items and urls, etc that this items depends upon """
-> 2995 return self._portal.get_item_dependencies(self.itemid)
2996
2997 def dependent_to(self):
/opt/conda/lib/python3.5/site-packages/arcgis/_impl/portalpy.py in get_item_dependencies(self, itemid)
1124
1125 def get_item_dependencies(self, itemid):
-> 1126 return self.con.post('content/items/' + itemid + '/dependencies', self._postdata())
1127
1128 def get_item_dependents_to(self, itemid):
/opt/conda/lib/python3.5/site-packages/arcgis/_impl/connection.py in post(self, path, postdata, files, ssl, compress, is_retry, use_ordered_dict, add_token, verify_cert, token)
954 elif errorcode == 498:
955 raise RuntimeError('Invalid token')
--> 956 self._handle_json_error(resp_json['error'], errorcode)
957 return None
958 except AttributeError:
/opt/conda/lib/python3.5/site-packages/arcgis/_impl/connection.py in _handle_json_error(self, error, errorcode)
974
975 errormessage = errormessage + "\n(Error Code: " + str(errorcode) +")"
--> 976 raise RuntimeError(errormessage)
977
978 class _StrictURLopener(request.FancyURLopener):
RuntimeError: Unable to get dependencies for item: item
Unable to retrieve item dependencies.
(Error Code: 500)