This forum is to be used for all discussions pertaining to Obsidian Entertainment's Neverwinter Nights 2, the Mask of the Betrayer expansion pack, the Storm of Zehir expansion pack, and the Mysteries of Westgate adventure pack.
I had the same problem. NWN2 installs .NET for the toolset but it is the 32-bit version. You need to install .NET for a 64-bit OS, I can't remember the exact URL, just google it and it should get you up and running .