As Makoto said, 401 seems like you have lost priviledges to access through your OAuth token so I would double check to make sure your app is still available and that your tokens are correct. You can check on the Your Apps Page.
Also, I noticed that your url seemed a bit different than what the SC api shows. Once you resolve to get a proper track id, the convention for a stream url is:
http://api.soundcloud.com/tracks/{id}/stream
This can be found in their track documentation.