(URGENT)Getting the USerName

I am developing an NT Service using ATL. In that Service I have to call an application. I am able to do that. My problem is when I am calling the Application from the NT Service it is taking the user name as “SYSTEM”. I Used the function “GetUserName” in the service and in the Application also. In Service it is returning correct user name i.e. my User name, where as in Application it is giving “SYSTEM”. If I run the Application individually, then it is giving correct user name i.e. My user name. I used “CreateProcess”, “_spawnl”, “ShellExecute”, “WinExec” all these options to run the Application from the service. Still no use. Can any one help me out. It is very urgent for me. Any help is highly appreciated.