http://www.nintendo.com/consumer/wfc/en_na/ds/results.jsp?error_code=001-0804&system=3DS&locale=lang
Unfortunately, but the 001-084 error code doesn't really give much useful information other than to say that "the Nintendo 3DS is unable to connect to an Access Point."
However, it does mention things like making sure that the "Nintendo 3DS system is within 30 feet of the wireless access point" and that "there is no interference from wireless phones".
So if the information at the above url and copy&pasted below doesn't help, perhaps you might want to give a call to Nintendo's 1-800-255-3700 (6 am ~ 7 pm Pacific, everyday) Customer Service number, and the service representative can do some over the phone troubleshooting to determine exactly what the problem is and then talk you through any needed steps to correct this.
The Nintendo 3DS is unable to connect to an Access Point. What to do will depend on where you are connecting from:
- Make sure that the Nintendo 3DS system is within 30 feet of the wireless access point and facing in its general direction.
- Make sure that any other interfering devices, such as microwaves and cordless phones, are turned off.
- Ensure the Hotspot location does not require an internet browser to setup an account, accept a use agreement, or enter a password before accessing their Wi-Fi service. If the location requires any of these items, you will not be able to connect to the internet with your Nintendo 3DS system.
- Make sure that the Nintendo 3DS system is within 30 feet of the wireless access point and facing in its general direction. Signal strength can vary, depending on where the access point's signal is coming from. (Please do not sit or stand in places that will interfere with the location's customers or staff.)
- Orient the Nintendo 3DS so that your body or other objects (such as walls, plants, furniture, and other people) are not blocking the signal. Also, make sure there is no interference from wireless phones (cell phones are okay).
- If the connection continues to fail, this Hotspot may have their router set up in a manner that is not compatible with the system. We recommend trying a different location.