Error 018 HELP

[Helaris]

Hello, sorry if the post is in the wrong place but I didn't know where to start it!
So, whenever I try to go and visit somebody (for trading villagers, items and co.) or others try to visit me, the 3ds gives me this message "error 018". I've tried EVERYTHING I could imagine, like, closing the firewalls, putting my connection to dmz, giving personal ip address to both (ds and connection) but nothing happened.
I've tried also the most stupid things, like, going the most close to my router...
Does any of you know any solutions?

 

[Sanaki]

Maybe your wifis aren't compatible? I've had someone who just couldn't connect to my town because of her company's wifi.

 

[Helaris]

Oh... it happened two times that I could go to another player's town and I've adopted two villagers! I really don't know what to do.