US任天堂のサイトの説明では主に電波の問題ですね。
Low battery power on the Nintendo DS (the light changes from green to red when battery power is low).
Signal strength from the access point is low. Move closer and try again.
Check for wireless interference. Devices such as cordless phones and microwave ovens should not be in use.
コードレスフォンとか電子レンジとか。近隣から何らかの接続を妨害する電波が漏れてるとか…