Natalia will send you the key again in a few minutes - it may have become corrupt when we sent it, or when you received it.

Just to clarify - I'm sure that you tried to enter the keys manually, but did you first try to replace the nwncdkey.ini file with the one we sent you? This may have been what you meant by "tried to replace the original one", but I'd like to make sure. :)

Also, I would strongly suggest uninstalling the game, installing it again and replacing the nwncdkey.ini file before applying any modifications to the game.