Yesterday I downloaded the MH4U demo from the Nintendo store, played solo for a bit, and then tried to set up a hunt with a friend online.
I created a Hall to hunt Tetsucabra, added a passcode, and sent my friend the Hall ID.
When he tried to join, it asked him for the passcode, accepted it, and after that he said it threw an error. So we reversed the process; he created a Hall and I tried to connect. Same deal. Error 006-0612, please try again later.
As per the Nintendo support link, we tried changing our 3DS' DNS settings to Google DNS on the off chance that helped. We tried the same thing (I created a hall and he tried to connect, then vice-versa) and got the same result.
Then I found a Chinese post that I do not fully understand, but seems to suggest setting your 3DS to your router's DMZ. I cannot do this, as the 3DS requires that it have a static IP when set to the DMZ, while my router requires than any device set to the DMZ have a dynamic IP.
Anyone else know where to go from here? Aside from buying a better router.