problems starting a msi file from an application: security message does not appear!

Hello,

On: Vista Home Basic, User with restricted rights

I want to start an msi file from an appplication (done with VB6).
Here is my line of code:
shell "%windir%\system32\msiexec.exe /i ""c:\Program
files\mypath\mysetup.msi"" /passive", vbNormalFocus

The line is executed and the msi file is started.
but the USC message does not appear, as it appears when typing in the
command line in a cmd window or double clicking at the msi file.
Though the msi file is executed not with admin rights and does not install
anything.

I tried workarounds with shortcuts, calling a the command line via cmd.exe,
....

How to solve this?