I posted my problem at WoT german forum and go a lot feedback of people having the same issue.
One of them asked if I use Kaspersky. He met the nail on the head.
Well, I am glad to say:
Problem found and solved.
Kaspersky Antivirus 2015 on my PC blocked this funcation from time to time.
Sometimes the first attempt was allowed, second try not.
I unistalled KAV 2015, rebooted and the problem was solved.
Then I wonder if KAV 2016 will re-create the problems but it didn't.
Until now KAV 2016 let me send message again.
Thanks for all supported me with your ideas.