Blank App: Security not working

Hi
in my Project i have a blank application to receive some ajax stuff. I want to use security to only users with valid logins can use this script.

When i turn on “security” in my blank application, i always get “invalid user” when i call the application.

And YES, i synchronized my apps and set all the rights for my blank application for the loged in users.

Is that a bug or do i something wrong?

Best regards
Steve