Access denied during Word Automation services / System.ServiceModel.Security.SecurityAccessDeniedException

I have added

using Microsoft.Office.Word.Server.Conversions;
using Microsoft.Office.Word.Server.Service;

I have created service application also the Word Automation Service is working on the server,I am also the Farm Admin

Reference :

http://msdn.microsoft.com/en-us/library/office/ff742315(v=office.14).aspx

I am using the first piece of code from the above link

Getting error at            job.Start();

Error : Access denied - System.ServiceModel.Security.SecurityAccessDeniedException was unhandled by user code

Please help