Wizard buttons missing

Hi all,

i managed to get an installer running on my machine. 

On my machine i used:

1.) The online installer for Windows for QT (https://www.qt.io/download-qt-installer?hsCtaTracking=9f6a2170-a938-42df-a8e2-a9f0b1d6cdce%7C6cb0de4f-9bb5-4778-ab02-bfb62735f3e5) (QTCreator 4.5.1 and QT5.10.1)

2.) https://download.qt.io/official_releases/qt-installer-framework/3.0.6/[QtInstallerFramework-win-x86.exe]

So i started to modify online example and it´s running fine on my machine.

Now i tried it on a Server pc (no QT installed) and the Buttons in the wizard are missing (see Picture)

So what can I do?

Have I forgot any property?