Can you check what build of the patch SR1 you have installed. From the date, I think it was the first version of the service release and I am not seeing the problem here using SR1b ("brazil_2.0_x86_20101220_SR1b") which is available in the download section. That would be the first thing to check on as the area light scale should be available to you.
you are right. I just update this and the parameter of area light scale works now. Thank you very much!!