Finally I found the solution:
the problem was that I am using
the router from my ISP (Pirelli PRGAV4202N)
my own router (Asus RT-N56U), with which I built my wireless network, and which is now set as Access Point, because there was also an issue with Double NAT.
Windows Firewall was switched off, also my ESET was not the problem, as I set up a rule for port 52199.
I now set another rule on the Pirelli router for opening the port 52199 on the Pirelli - and Voila! Here it goes, my new remote control, aka Samsung SGS2 Android mobile phone!
The only issue what I didnt understand yet so far is, if I am opening ports on a router - isnt there a security issue with that? Also, I would prefer the router functionality of my Asus instead the Pirelli, but with avoiding having double NAT.
But thats something I dont want to bother you with - maybe I should check other forums for that...
Thanks for your great help