This also just started occurring on our builds. Was working fine last week. Node version 4.3.2.
npm info attempt registry request try #1 at 10:03:21 PM
npm http fetch GET http://packages.appdynamics.com/npm/4.2.1.0/appdynamics-native.tgz
npm info retry fetch attempt 2 at 10:03:21 PM
npm info attempt registry request try #1 at 10:03:21 PM
npm http fetch GET http://packages.appdynamics.com/npm/4.2.1.0/appdynamics-zmq.tgz
npm http fetch 403 http://packages.appdynamics.com/npm/4.2.1.0/appdynamics-native.tgz
npm ERR! fetch failed http://packages.appdynamics.com/npm/4.2.1.0/appdynamics-native.tgz
npm WARN retry will retry, error on last attempt: Error: fetch failed with status code 403
npm http fetch 403 http://packages.appdynamics.com/npm/4.2.1.0/appdynamics-zmq.tgz
npm ERR! fetch failed http://packages.appdynamics.com/npm/4.2.1.0/appdynamics-zmq.tgz
npm WARN retry will retry, error on last attempt: Error: fetch failed with status code 403
npm http fetch 403 http://packages.appdynamics.com/npm/4.2.1.0/appdynamics-protobuf.tgz
npm ERR! fetch failed http://packages.appdynamics.com/npm/4.2.1.0/appdynamics-protobuf.tgz
npm WARN retry will retry, error on last attempt: Error: fetch failed with status code 403