it seems that I solved the problem for myself. There is a manual dialer for manual/single/continous AF. When it is set to continous, capturing will not work from Liveview. If set to single AF, it works fine. This morning I remembered that I had similar problems with a yongnuo wireless remote control when the camera was in continous mode and retested it.
Thanks for your quick reactions.
Regards
Jürgen