I don't think you can convert 2004 AutoCad file using a 2002 AutoCad. On the other hands, AutoCad 2004 can convert 2002 without any problem but not vice versa.
If you run into this problem again, be sure to tell the person who is using AutoCad 2004 to "SAVE AS AutoCad 2002 version" when he/she is finished drafting. This way, you don't have to face this problem again.
As of now, the only solution, is to send it to someone who has AutoCad 2004 as mentioned by Hoja so he/she can convert it for you.