There is currently an outage of the Google Drive System. Google is aware of the outage. When the issue is resolved, it will be listed on the Google Apps Dashboard.
Remember that should you ever notice an issue with a Google service, you can check the status of that service at the Google Apps Dashboard.
This outage is affecting Google Drive, Docs, Sheets, and Slides.
UPDATE 5:30PM 10/9/15: Issue resolved by Google.