Adding an Azure subscription to App Controller - Service Unavailable

I noticed today that I hadn't re-added my Windows Azure subscription to my App Controller deployment in my testlab and so clicked the link on the overview page to add it back.
After entering the relevant details such as Subscription ID, Certificate pfx file and password, I was greeted by a not too helpful error message of "Service Unavailable" with no further details.

 

After scratching my head and trying several things such as deleting the certificate and re-adding it to Azure, checking firewalls etc I remembered this server had just had a restart.

 

I checked the services to make sure everything had started up ok and noticed that the App Controller Windows Azure Provider service wasn't started.

 

 

I started the service, tried adding the subscription again and voilà! It works.

 

I hope this helps someone else if they get this generic undetailed message.