You need to start in Bryce 5.01 Render and then save and Open in 5.5...Then render and save then run the same Test backwards open the scene in Bryce5.5 first render and save then 5.01 and save...Now if you use Lights in 5.01 then you need to turn off the Gel light in 5.5 when doing this test Because of the Gel light Bug that was fixed in 5.5...