Hi folks,
I figured the problem out myself and in case someone else encounters this problem, here is what worked for me:
I ran dependency walker and only found dependencies on Core, Gui, QML, Quick and Widget (which I included in the folder of the executable).
Apparently what was missing were dependencies for
Multimedia, MultimediaWidget, Network, OpenGL, Positioning, PrintSupport, Sensors, Sql, WebChannel, WebKit, WebKitWidgets and the QtWebProcess.exe. I have no idea why this would be needed or why the error message did not say anything about it but it silently worked when adding these libraries to the folder of the executable. I followed these "deployment instructions":http://qt-project.org/wiki/Deploy_an_Application_on_Windows to figure out which libraries were necessary. Sadly I did not find any documentation about which modules have which dependencies so there is only the trial and error method described there.
Best Regards,
Jan