I have found a lot of threads on the "Failed to get available update data" error, but I have yet to find a solution.
My Drupal 7.16 installation fails to get status updates on modules or the core update.
I am able to run cron from the server. That does not seem to be an issue.
It appears to be a very common problem, so I am a bit confused on how I can't seem to find someone who has solved it.