DSTT wifi not working

Suddenly, my wifi isnt working anymore. It's really weird. When I put an original DS cartridge in my DS, it can find wifi access points. But when im setting up wifi connection using DSTT it says: The access point's settings are not supported by the Nintendo DS. And when I play pokemon black and look on the C-gear it says there is wifi but when i want to battle online i get an error. What to do?

your ds probably doesnt support that form of wifi i had the same error but my internet protection was too modern for a ds game to connect to even though my dsi could

Your Router setting have to be change to Open (WEP)