ok  super noob here . my friend bought me a copy of the game 8). and we have the same mods all the same junk  and we were able to play threw lan  but  now he has moved so we are no longer in the same room  and  we can not figuer out how to play. always says sesion can not be found/doesnt exist anymore    so can anyone help ? would be awesome if you could and i hope i asked this question in the right section 

Is it through Steam? If so, you should be able to invite your friend in the Steam client. If it's the disk, than download a program like LogMeIn Hamachi to connect to each other without being on the same internet.

Is it a bought copy or downloaded?

my copy is from steam  his copy is the bought disk he has all the updates and what not i havent bin able to get hamachi working but if i do how would i connect.  would i just get us in the same room in hamachi then lan search in game ???