I found something in the world wide web, it might be interesting!
I don't know for it's your domain, but i just want to inform you.
But look at that site, Sinteria.net, HERE
Dude i already checked all. I think its a problem on your side. You 100% have Client 8.50 not 8.52? you have the right IP-Changer for 8.50 and you already choose 8.5 on IP-Changer? you used port 7171? Copy and past exactly:
Sinteria-Firestorm.no-ip.org
and test login.
If it dont work make a new char and test it again.
Go on Options at Asprate's Multi Ip Changer, and take the marks at Lauch with Gamemaster and test server away.