[giacob]

WITH eMITTERS PLASTER looks BLACK
WITHOUT them looks WHITE
(sorry for caps)
it seems have not esplanation whatsoever

plaster is just diffuse material with bump map (rgb)

[Maxer]

What are you using for emitters, planes?

[giacob]

i am using boxes

[Maxer]

Try flipping the normals of your boxes.

[giacob]

it shouldnt be a problem of flipped normal because if i put another material it works... i mean if i put travertine instead of plasterin the multi subobject material

[Hervé]

maybe you have luminosity set to 0... remove the emitters you don't use... otherwise they'll suck the light... I recall someone had a similar problem...