Exception using Google.GData.Apps : The remote server returned an error: (503) Server Unavailable

See more:

C#

C#4.0

google-app

I am using google provisioning api on my website. I want to authenticate user using AppsService class.

AppsService service = new AppsService("domain", "admin username", "admin password");
UserEntry user = service.RetrieveUser("username");
But it throws exception: Execution of request failed: https://apps-apis.google.com/a/feeds/pmu.mygbiz.com/user/2.0/username

InnerException is: The remote server returned an error: (503) Server Unavailable.
It was working before 6 months ago