Expect service interruptions on February 25 and 26.
Nintendo has stated on its Network Status page that "emergency maintenance" is scheduled Monday, February 25 and Tuesday, February 26 for the online portions of Pokémon Black and White (both the originals and sequels), Ninja Gaiden 3: Razor's Edge, and Warriors Orochi 3 Hyper. Nintendo has not specifically discussed what needs fixing, but expect intermittent issues with playing any of these games online on February 25 and 26.
Pokemon Black and White (2) maintenance is planned to start on Monday at 11 p.m PST and will end on Tuesday at 5 p.m PST. Ninja Gaiden and Warriors Orochi will have a much shorter maintenance period, occuring on Monday between 4 p.m. PST and 5 p.m PST.