I know i know, this is an old error and a lot of people resolved it by :
1-Turning on UPNP.
2-Deleting Game settings.bin.
3-Disabling firewall.
And others, but for some reason NONE of the above helped me i was sick of keep trying more and more useless things, so searching on the web i found this solution and it might be helpful for people (SOME) that has this little problem.
(btw this happened to me and my friend when we were playing for like 10 or so minutes on any server and then boom there goes the error)
Link to the fix = http://rawgamingnation.com/index.php/to ... been-lost/
Sorry if i posted this in the wrong section, sorry if i did something wrong, it is my first time on this forum and i just wanted to help.
Greetings, Ariel.