If this helps, I had the same problem. I was using ClusterLayer.js via a dojo.require("extra.ClusterLayer"); Within this file, (ClusterLayer.js), there is a dojo.declare("extras.ClusterLayer", esri.layers.GraphicsLayer, { ....etc...}); What solved my issue was adding, to the top of this file, dojo.require("esri.layers.graphics"); reason being that this file was expanding GraphicsLayer without first added the the sub class first. Not sure why this worked on earlier versions though.