The Access Point you are attempting to connect to is not compatible with the Nintendo Wi-Fi Connection, and is likely at a non-partner Hotspot.
If you have multiple connection files saved to your Nintendo DS, the error message you received can help determine which connection file may be experiencing a problem:
Please try to find another access point.
If you are attempting to connect through your home wireless network, and are receiving this message, your router may not be compatible with the Nintendo WFC. Click here for a list of supported routers.
If the above information does not work, and you are using the Nintendo Wi-Fi USB Connector, click here for additional assistance.
If the above information does not work, and you are connecting at home with a wireless router, there could be some settings on your router that need to be adjusted. Please click here for more information.