Something may have gone wrong when you first installed NwN causing a corrupt mss32.dll.  If that's the case (and that is a BIG "if"), you can try to copy the Mss32.dll directly from the Windows_data.zip on the DVD (assuming you are using the Diamond game version) to the respective NwN folders.  Take note that there appears to be two locations where it gets installed  (NWN and NWN/miles) and there are two distinct files in the zip with the same name.  Whether there is any difference between them, I can't tell you, so would be best to place each one separately in the corresponding folder.
Another possibility (without knowing anything about your current installation) is that you may have DL'd the wrong Critical Rebuild for your game version.
If it is NOT a corrupt dynamic library file, please simulate a Tech seat at your machine by displaying your full system specs as recommended
here.  The more thorough you are, the faster the community will be able to make effective suggestions to get you operating properly again.
Good luck, mate!
Modifié par HipMaestro, 25 août 2010 - 12:42 .