Woned

Resolved: Ran all 3 games (Arma 2, OA, CO) on both steam accounts - afterwards this caused my brothers computer to not be able to join ANY games so I followed http://dayzmod.com/forum/index.php?/topic/45202-fix-for-being-kicked/ and it resolved his issue. We can both play now woohoo! Thanks for the tips guys.

Well I ran all 3 again on both computers and now his is just not connecting to any server.. i'm redownloading six updater on his computer and testing again

Tried doing what you said but we still run into the same issue... comes up with "You have been kicked from the game" as soon as he joins the same server as me

Before he had bought the game I downloaded the game onto his computer using my steam account and played some games through Six Launcher.. not sure if this may cause an issue?

The only thing I see related at this point is our internet connection...

Yes, we have separate copies of the game on separate computers and steam accounts

My brother and I can join any two separate servers perfectly fine and everything works but if he joins a server I am currently connected to it just says "You have been kicked from the server". If he joins first and I join second I receive the error message. We updated our Six Launcher (automatic) and Arma 2 + Operation Arrowhead through steam. We tried setting port values through steam for Arma 2 and OA through launch options but this had no effect. Also tried just joining the same server in Arma 2 (not dayz) and it worked fine. I think it may be due to us having the same IP address though I'm not sure... If anyone has some insight as to what we can try to resolve this I'd appreciate it.