We are having proxy server authentication for accessing external sites in our System. When tried to validate the proxy server with credentials from "manage plugins" section and "advanced" tab in jenkins, we are getting "Failed to connect to http://www.google.com (code 407)" error.
But those proxy server and the credentials and absolutely correct as they work from other tools. And strangely sometimes validation works(once in a while) and most of the times not.
I had attached the error that we get from the Tomcat logs and the screen shot from Jenkins.

Please let me know if you need further details,
Please address this issue and resolve this, we are facing this since many days

Regards,
Vamsi Hari