Did you try to add /IT
?
This is the only option which may allow you to display something on the active session using scheduled tasks. However, I am not sure that Windows will allow to interact with the desktop of another user.
Edit : You may use /RU BUILTIN\Users /IT
, so any user will be able to run it interactively. What is you constraint on /RU system ?
If your goal is to display the samp.txt file content when a user logs on, another solution is to put the samp.txt in the startup folder of the "all users" start menu : C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup