arcgis desktop - Writing world file when exporting TIFF using ArcPy Mapping?

According to documentation, the options are: Syntax

ExportToTIFF (map_document, out_tiff, {data_frame}, {df_export_width}, {df_export_height}, {resolution}, {world_file}, {color_mode}, {tiff_compression}, {geoTIFF_tags})

However, this works:

import arcpy.mapping
mxd = arcpy.mapping.MapDocument("CURRENT")
arcpy.mapping.ListDataFrames(mxd)
arcpy.mapping.ExportToTIFF(mxd,r"D:\out2.tif","PAGE_LAYOUT",640,480,96)

but this:

arcpy.mapping.ExportToTIFF(mxd,r"D:\out2.tif","PAGE_LAYOUT",640,480,96,True)

yields: Runtime error : PageLayoutObject: Error in executing ExportToTIFF

Am I doing something wrong with that Boolean for world_file?