I, like many others, had this issue. I went through all fixes listed here but it still wasn't working.

Then, on a lark, I updated my video card driver (which was recently updated). Lo and behold, NWN worked like a charm.

So if anyone is having issues, try this out as well. The source that recommended it also said that many newer cards had drivers that weren't compatible until more recent drivers were downloaded. FTR, my card is an ATI 5400.

Peace.