for users without admin privileges the Windows Update window stay freezy, like waiting for installThis mean that the EXE try to display a User Interface to the screen but "System" Account doesn't have such feature.
for users with admin privileges the window appears and the software can be installed successfully.If the EXE needs some informations to install the software, then the UI need to be displayed. In the "Update Creation Wizard", check the checkbox call "Can request user input".
Which software do you try to deploy ?