Yes, If I remove the special character "#" it works.
http://geocode.arcgis.com/arcgis/rest/services/World/GeocodeServer/findAddressCandidates?SingleLine=...
Response:
"candidates": [ { "address": "Pho So 1 Boston", "location": { "x": -71.043648798999641, "y": 42.163068841000495 }, "score": 95.5, "attributes": { "City": "Randolph", "Region": "Massachusetts", "Country": "USA", "Postal": "" }, "extent": { "xmin": -71.048649999999995, "ymin": 42.158068999999998, "xmax": -71.038650000000004, "ymax": 42.168069000000003 } } ]