I tried to install the full version of NWN and the validation code worked on the main game, but then balked - told me incorrect code - when I tried to install Undrentide. Just on a whim I tried the code for another NWN version I had and it ACTUALLY WORKED. Then it balked again when I tried to install HUD and I got it to work by using the code from a different HUD expansion. Is this bizarre or what? I'm running Windows 8. I had these versions installed before (but not currently) so maybe my computer remembered them or something. I'm just grateful I got the game working. I guess if you have this issue, try validation codes for other versions if you have them.