I'm not sure why you encountered the this behavior.
In order to have a better view about this, can you please send us the .AIP (project file) to support at advancedinstaller dot com so we can investigate it? If it contains confidential information you can send us a small test project which reproduce this behavior.
For everyone else having this problem: There was a "DatabaseFile_Cond" condition associated with the "Display a specific dialog" event (No idea how I putted it there). By expanding the tree of my dialog I could delete this condition and with this I could delete the event. The reason why the tutorial did not work was that I used the event "Display a specific dialog" instead of "Display a specific child dialog".