I noticed that the Wifi app doesn't start with windows. I had to start it manually, then it works no problem.
Don't forget, for those of you that it's never worked for, check your settings on your firewall.
Make sure that the Wifi app is allowed full access to the net.
Allow traffic to all destinations on ports: 28910, 29900, 29901, 29920, 80, and 443
Allow all traffic to all destinations.
If your firewall or PC security program keeps a list of trusted applications (also known as a "trusted zone"), the following programs are installed with the Nintendo Wi-Fi USB Connector, and require internet communications. If prompted by your firewall or PC security program, add these to the list of trusted applications. This information may also apply to certain computer security applications, such as anti-virus, anti-spyware, etc.:
Nintendo Wi-Fi Connector USB (NintendoWFCReg.exe )
Setup.exe (when installing the USB Connector)
"Trusted" IP Ranges:
There are also potential ranges of IP addresses that may need to be added to the "trusted zone" for your software firewall or PC security program for Nintendo Wi-Fi USB Connector users. Each of these would need to be opened up for TCP and UDP traffic, or for some firewalls or security programs, added as a "trusted zone." Please consult the manual for your firewall or security program for more specific information.
192.168.1.1 subnet mask 255.255.255.0
172.16.1.1 subnet mask 255.255.255.0
0.0.0.0 subnet mask 255.255.255.255
Check your settings, and make sure the Wifi app is still running!!