Nintendo has warned owners of Metroid: Other M of a glitch within the game that keeps a door locked. The fix? Send in your SD card.
Kotaku report that owners of the game might be experiencing an error in sector 3 where a door remains red and locked. In order to fix the issue if you've already saved, you'll need to copy it onto an SD card and send it in the mail for Nintendo to fix.
For more details see the Official Metroid: Other M error page.
Have you encountered any strange errors in your game? Should having to send your save file to the publisher be the way - or should it really be a case of a quick downloadable patch?