If you are using Hangouts on Air to broadcast live on Google+ & YouTube and facing difficulties then you may not be alone. There is a partial outage going on with these services and Google+ team is actively working on it.
If you are seeing stuck at preparing broadcast stuck at 99% for a long time, then you are not alone.
Here is outage notification from +chew chew of Google
we’re still seeing partial outage of live streaming for hangouts on air and youtube. we’re working on it as quickly as we can. sorry for the outage.
We’ll update as soon as we hear from Google+ team.
Team still working on it. Seeing a few streams starting here and there, but not staying up yet.
Update #2 (Final)
+Chew Chew of Google+ confirmed issues are now resolved and services are back to normal, up and running.