[Paraview] Generating normal color map

[the lily]

Dear all
I wrote a script that generats color map using normal and then color the surface with it
the script works fine for some data while it displays the following error 
message for other data 
ValueError: Could not locate array Normals in the input.
this is my code
	a1_Normals_PVLookupTable = GetLookupTableForArray( "Normals", 3,NumberOfTableValues=2048 )	a1_Normals_PVLookupTable.RGBPoints=[-1.0, 0.0, 0.0, 0.0, 1.0, 1.0, 1.0, 1.0]	a1_Normals_PVLookupTable.Discretize = 0
	# We want x component of the normal	a1_Normals_PVLookupTable.VectorComponent = 0	a1_Normals_PVLookupTable.NanColor=[0.0, 1.0, 0.0]	a1_Normals_PVLookupTable.ColorSpace='RGB'	a1_Normals_PVLookupTable.ScalarRangeInitialized=1.0	DataRepresentation0.ColorArrayName = 'Normals'	DataRepresentation0.LookupTable = a1_Normals_PVLookupTable	DataRepresentation0.InterpolateScalarsBeforeMapping = 1
 		 	   		  
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