Applying graduated color symbology using arcpy.mapping?

Question

I am trying to apply a graduated color symbology from one layer to another. The script adds a layer to an mxd but foes not apply the symbology from the symbology layer.

Can someone tell me what I am doing wrong?

This did work a few days ago for other layers but is no longer working.

This is the script, path names modifiied

import arcpy

arcpy.env.workspace = r"C:\Workarea\BrandiS"

mxd = arcpy.mapping.MapDocument(r"C:\Workarea\BrandiS\SymbolTest.mxd")

df = arcpy.mapping.ListDataFrames(mxd, "Layers")[0]

featureLayer = r"C:\Workarea\BrandiS\TestLayer.lyr"

addLayer = arcpy.mapping.Layer(featureLayer)
arcpy.mapping.AddLayer(df, addLayer, "TOP")

if addLayer.symbologyType == "GRADUATED_COLOR":
   addLayer.symbology.valueField = "Join_Count"

symbolLayer = r"C:\Workarea\BrandiS\SymbolLayer.lyr"

arcpy.mapping.UpdateLayer(df, addLayer, symbolLayer)

mxd.save()

del mxd, df, featureLayer, addLayer, symbolLayer