first....very nice render...well minus the defect...but great render anyway...nice effects with light, texture, and displacement.... about the defects....i get a similar trouble with single sided plane primitives (especially the vertical plane) with spotlights....the problem is when i point a spotlight at a vertical plane primitive i end up with grey and black checkerboard patterns....turning off the smoothing doesnt help...the solution i discovered was to replace the plane with a resized square primitive....the checkerboard patterns disappear if i use anything other than a plane primitive...this pattern shows up on a plane whether textured or not as long as a spotlight is used.....i wonder why.... i thinks its probably what ynsaen said about the geometry.... anyway.....i thought id mention it.....its kinda like your problem.... i guess if its possible you could replace the affected areas in your scene with a resized square primitive? or export a poser square primitive and incorporate it in your original mesh... if all else fails you can always use photoshop to cover the defects....