We have developed two applications
Twitter Update Plug-in for Windows Live Writer using oAuth
Geekiest Social Media Updater
Both were showing 404 Error ( The remote server returned an error: (404) Not Found. )
when trying to update twitter status. The issue was that we were using http://twitter.com/statuses/update.xml and changed it to https://api.twitter.com/1/statuses/update.xml and the issue solved. Updated the applications and if you were using any of these, you can update them now.