The problem: I was getting this error in the IIS 7.
HTTP Error 503. The service is unavailable. The solution: I tried browsing my website using IIS or restarting my IIS but this problem was still there, then I noticed that your application pool is stopped, so restarted the Application Pool and the problem is gone.
So when you also face the same issue, do this trick !
Regards,
Sheo Narayan
http://www.dotnetfunda.com