WorkItem Store returns null and throwing Not an authorized Error

We need help on the following. In case you have a solution to propose please reply only to Loka who is marked in the email.

We are developing a class library in C#.Net, which will perform the Integration of TFS (Team Foundation Server)  to Remedy Force.

Problem: We are trying to retrieve the work Item’s (Task’s ) fields using

TfsTeamProjectCollectionFactory. GetTeamProjectCollection method and able to do so from my System and also from Virtual Machine where TFS was installed which is a TFS Server using  a Console Application.

But when we are trying do the same using a class library from a Virtual Machine where TFS was installed which is a TFS Server, we are getting null in WorkItems collection.

Query:

-          How can we retrieve the work item collection in a class library project as in conole Application .

-          What are the settings to be checked in VM.

NOTE : In VM the OS is  windows 2008 Server R2 where as in my system. it’s Windows 7.