incorrect serial key!

when I try to get into nw server I got a incorrect serial key I tried everything from restart steam to reinstall nw,
when I tried to regedit it, the nw seriel key was empty and when I filled it,exit and enter again it was still writen but when I get into the game and get the error again and then go to regedit it got empty again!
when I tried register the nw key in tw it workes so the keys need to be work why it doesnt work??
what to do plz help

Lots of people seem to be having this problem right now, we don't know what it is caused by yet nor what to do about it. 

Have you seen the next thread on the board? It's about exactly the same problem so next time just reply to that thread instead of making a new one.