YouTube.com, and by extension the YouTube API, will be in read-only mode on Monday, September 17 starting at 8:00pm PDT. This should last for approximately 2 to 4 hours.
YouTube API calls that create or update metadata or videos will fail during this period of time. As a best practice, we recommend making sure your code gracefully handles service errors on POST/PUT/DELETE operations:
-Jeff Posnick, YouTube API Team