Why when I try to call friend with Skype the Internet connection quit?

[Ssssss]

I have a lot of friends with whom I use Skype, but only with one when i try to call the Internet connection shut down. Doing the call with the same friend on Yahoo Messenger have the same result.
I saw many have that issue and I tried all suggestions, but nothing is working.

[Decy Ja]

With the information provided, it is hard to outline the exact issue, but it might have something to do with how you connect with internet, or some 'protector' app running on your computer, or at the ISP's end, that 'sees' the IP address of that friend to be potentially malicious, and as a way of preventing an intrusion it cuts down the connection. One of the things you can do is call your ISP and ask them to provide you with a feedback about why your connection has dropped at an exact time you specified.