I just installed TeamSpeak again on a ubuntu machine hosted by OVH.

My problem is kinda strange and I have not found anything helpful over the web and so I hope that somebody here might be able to help me out with that annoying problem.

First, the settings are all default. A fresh install.
When I try to connect everything seems to be fine.
Now if some friends try to connect they only receive the message: "Failed to connect to server".

The thing what makes it strange is that if they open putty and establish an ssh connection to the ubuntu machine and connect to the TeamSpeak via the client while the ssh connection is opened it works fine for them.

They don't even have to keep that ssh connection opened. If they close the ssh connection they are still able to connect to the TeamSpeak. They have to do that just for the first connection for some reason.

I have no idea where the problem is.

I hope somebody can help me with that annoying problem.
Thanks much for your time.