http://www.nintendo.com/consumer/wfc/en_na/ds/results.jsp?error_code=20109&system=3DS&locale=en_US i hope this helps.

It might be because you are playing a DS game, those do not support certain types of internet, if you don't know if it is supported try going to the DS game itself and going to connection settings and try searching for a connection, it will tell you if it is supported or not. I hope this helps.

Ashika-

First, please start a new thread when you have a problem. If you revive a 7 month old thread, there is very little chance that someone will see and respond to your post.

Second, do you have any security enabled on your router? Though the 3DS and 3DS games support WPA level security, DS games in a 3DS will NOT work with a WPA or WPA2-encrypted router.

@ Hoodoo, try if any other games work with the wi-fi. If not, you may want to repair it.

I have exactly the same issue with my 3DS when trying to connect to Nintendo Wi-Fi Connection using Pokemon Black or Pokemon HeartGold.  Accessing Nintendo WFC worked fine before I sent it in for repair.  Everything works fine if I use the games in my old DSi, and my 3DS has no trouble with regular internet access or playing Super Street Fighter IV 3D online. The Nintendo rep I spoke to said I'd have to send my 3DS back in for repair but didn't have any information on error code 20109.  Did anyone who's been through this before get any insights as to the cause?  I'd be very surprised if this is a hardware issue with the 3DS itself.

Yes.  I connect through my router (which has WPA security) with Pokemon Black, while I have a laptop that I temporarily set up as a WEP Wi-Fi node so I can connect with Pokemon HeartGold without having to downgrade my router's security.   I get the error code either way.  I was at Nintendo World earlier today where they have no security on their Wi-Fi at all, and I still got the error in Pokemon Black.  The only other unusual thing I noticed when I got my 3DS back from repairs is that its Nintendo Wi-Fi Connection ID is now blank when I look under System Settings > Internet Settings > Nintendo DS Connections > Options > System Information.  I must have had an ID, or I never would have been able to connect to Nintendo WFC with HeartGold.  My hypothesis here is that the ID somehow got wiped as part of the repair process, Nintendo WFC likely keeps a database of 3DS's and their IDs, and Nintendo WFC boots me off because my 3DS is already registered but no longer has the ID it was assigned.

I hate to send my 3DS back again for something that seems unlikely to be a hardware problem, but Nintendo USA didn't have much of any troubleshooting options for error code 20109 (or much of any information on what the error code actually signifies).