Google Spreadsheet Feed and new Google Sheets
Do you know that you can easily get list of all your documents stored on Google Drive? You can use URL like https://spreadsheets.google.com/feeds/spreadsheets/private/full and you will get feed of all your spreadsheets. There's more URLs like this... Cute, isn't it? The bad part of this is that it shows you only "old-time" sheets, not the new ones which were launched in December 2013. It's still unsupported feature according to Google Support. I wish I knew that before yesterday's night: the feed contained sheets I created few days ago, but not the one from yesterday.
What does that mean to you?
You can't edit this file via Spreadsheets API, that means directly from command line or using any of existing libraries and tools (like gspread or gdata-python-client).
Workaround
To get over it, try to disable new Google Sheets completely (they mention unsupported API there too, dammit) or just duplicate one of your older document, created before new Sheets...