MK7 just says Searching for players dut doesn't find a thing

Hi,I bought Mario Kart 7 today, and I tried to go online, but it just says searching for players for a long while and then it says it has a communication error after which it just goes back to the mario kart menu.
It is the first game which can go online on my 3DS but with other things like the internetbrowser or the eShop it doesn't have any problem.I am connected via a wireles router with WPA-TKIP encryption
My OS is 3.0.0-6E
(I think my MKWii has the same problem but we always thought it was because the disc was scratched)Edit: Joining persons out of the 3DS Friends list, gives the same problem.
Can anyone help me? I kinda bought it for the online mode.Thanks in advance.

I think I know what the problem is now, my router doesn't have a DMZ option. Does anyone know if it will work when I buy a WFC usb stick and channel it through my PC?

if a DMZ is necessary (unlikely) the running it through your PC will make no difference at all

I hate my provider now.
Because people on the interwebs who have the same problem could solve it by putting the IP of the 3DS, inside, or outside(I don't know which of the two) the DMZ.
But the router our provider gave us doesn't have the option to alter the DMZ at all :@