I have a few suggestions that may help but im not an expert or anything.
1: check your NAT type is open. I had problems with this in the past. Some games dont seem to care about it but others seem to be very buggy with Moderate or Strict NAT type settings.
2: Check NW is updated to the latest version.
3: If the above dont work try reinstalling NW.
4: Make sure your copy of NW is legitimate and the CD key hasnt been shared with anyone else.
Hope these suggestions help. Good luck getting it fixed and getting back ingame