Working on my latest pic using spectral atmos/render mode GI or GA when I preview the scence via preview render mode it looks fine....When I up the quality to final and above the pic becomes very dark & doesn't even remotely look like the preview render.  I can't brighten the pic using the balance slider as then the textures become almost glowing & washed out. This has happened in fact with all the pics I've done, but this one to date is by far the worst case scenerio.

Why is this happening?  Have I missed a setting? Or is this a bug?  This is totally frustrating :(

Thanks :)