I think I may have found the problems I was having using Area Lights in Blender when rendering with Yafray. It seems that if you turn the area light into a rectangle instead of a square the light fails to work. Putting the light back to a square makes it work again, of coarse you have to turn the energy up to make it show up. In the Blender renderer I keep the power at 1 with a distance of 8. As Yafray as the renderer it does’t make a difference what the distance is, but the energy must go to 4.
EDIT: Also turning on photons makes the scene render black.
I didn’t change the light, just added the photon section in Yafray render settings. It works perfect with Spot or Lamp. It is just a problem with Area Lights, so there is a bug in the way they send that info to Yafray. You shouldn’t have to edit the XML file to get a light to work, that is a bug.