This is getting ridiculous. I have been trying to connect with multiple DSs (mine and my sister's) for days now to our router, but no luck. I have the router key and on the very rarest of occasions (literally, about 1 out of 100 times) it will connect, but otherwise it will provide me with either a 52100 or 20100 code. Now, most recently, it has started giving me nothing but the 52000 code, and I'm right next to my router. Please, I'm begging someone to help me. I don't want to have to go over to friends' houses every time I want to play pokemon or something like that with my out-of-state friends. In addition, I've checked and it appears I have a D-link router, which is supposed to work fine.
Look at these pages and try any troubleshooting tips listed to see if they help resolve your problem. If they don't work, then you should call Nintendo's Consumer Service Department at 1-800-255-3700 anytime from 6 AM to 7 PM Pacific Time, 7 days a week.
You can also use e-mail to contact Nintendo's Consumer Service Department.