This could be a client side error Jan. Try and reinstall nwn again, make sure you have the all the lastest Hak's. There was a update on the control hak yesterday, so make sure you get that aswell if you dont have it. If the problem still persists, I need a detailed report about what you do priot to this crashing.
Also if the other person that this happens to, could tell me, in detail, whats he or she does before this crash occours, it would help us alot.
Be sure to include what armor you trying to switch to and from, which modification you have done to it. What race, class you are playing. In which place does this happen.
Thank you in advance.