Oh yes, I've done all the virus scanning and such (I'm quite fastidious about such things). Its the actual NWN2 launcher which gives that error. Its just strange because its fine playing it for weeks and weeks, but this only seems to happen when I take the DVD out to play something else.
Though I should add that it still works if I open NWN2.exe or nwloader.exe, but won't if I open NWN2launcher.exe so it is obviously just this file that is associated with nwn.ini (the one that changes) - its just a strange thing to be wrong, its not as if the file is FUBAR, it just one letter that changes!
I'll see if reinstalling fixes it, but will wait until the weekend to do that as I'm lazy