TFS work item store is not connecting in production server using server side event handler code

Server side plugin code to connect to work item store

tfs = new TfsTeamProjectCollection(new Uri(tfsUri));
store = (WorkItemStore)tfs.GetService(typeof(WorkItemStore));

I used the above code and accessed work item store in my TFS DEV server without username and password. But the same plugin code is not working for the TFS Production server.

Exception:

Account name:
domain\TFSService Detailed Message: : TF30063: You are
not authorized to access http://localhost:8080/tfs/xx. Exception Message: TF30063: You are not
authorized to access http://localhost:8080/tfs/xx

Please guide