You need to launch a file as the System account to verify access rights, test network access, test LiveUpdate, look at proxy settings or to try to install using a non-user based account but have found the new security changes in the Microsoft Windows kernel 6 or greater prevents the AT task scheduler from launching an "interactive" application with system level access.
Changes in the Windows account security prevents direct access from the command line to the task schedulers ability to create a local session-0 interactive system account run applications. This issue will apply to any Windows operating system running kernel 6 or greater. (Vista, Windows 7, Server 2008, Server 2008 R2 for all 32-bit and 64-bit variants as well as Itanium.)
When you try to use the AT scheduler with the /interactive switch you will get the following window:
If you use the Windows built-in GUI task scheduler or the Schtasks tool, you will be able to assign the System account to launch the application but you will not be able to see or interact with the application now due to security changes in Windows. The application will show in the Task Manager but that is the total level of interaction ALL local users will get.
"Service Changes for Windows Vista," which discusses the changes in the security model: