YouTube categorization does not show up as expected under policy trace, and policies based on YouTube category do not match.

Testing a YouTube URL in Configuration > Content Filtering > General > Diagnostics --> Test results in an "unavailable" message.

Determine if the ProxySG appliance is exceeding the limit on YouTube API v2.0. Currently SGOS 6.5.x uses YouTube API v2.0 to determine categorization for a YouTube URL. It uses gdata.youtube.com/feeds/api/videos with a query string attached to the actual URL to determine the category. 

Complete the following steps:

1.  Go to the appliance event-log:
   https://<appliance_IP_address>:8082 /eventlog/fetch=0xffffffff
2. Look for any event-log that is similar to the following message:
   "Failed to fetch service url 'http://gdata.youtube.com/feeds/api/videos/PSMDPzd11ek?v=2&fields=media:group(media:category)'(HTTP 403 - Forbidden)"
   The existence of such a message verifies that the limit has been exceeded on the YouTube API v2.0.

You can also take a packet capture with the filter “host gdata.youtube.com”. If the limit has been exceeded on the YouTube API v2, the following behavior occurs:

The previous example shows that the API responded with HTTP response code 403 and returns an XML output message “too_many_recent_calls”.

As stated in the SGOS Administration Guide, this feature is provided on an "as-is" basis. Blue Coat has no control over the quota limits.

YouTube does not provide information on quota limits, but notes that there is an equal distribution for all requesters from different locations/applications; YouTube recommends that you wait and try again.
For more information, refer to  https://developers.google.com/youtube/2.0/developers_guide_protocol_error_responses.