Im having same problem, theres three of us, all tried hosting server and none of us can see any of each others servers. This is the prerequisite: On some DayZ Expansion servers you can build. Overall, Details really help, saying there's a problem without addressing the current configuration/setup ect. got to steam, right click arma, properties, betas then got to 1.62 older betas. Base Building Full Features List: - Ability to build 30+ Arma 2/OA Objects in. Official: v1.11 is available from Arma 2 Official Web Site Windows Official: v1.11 is available from Arma 2 Official Web Site From v1.05 and beyond the window dedicated server exe is part of the client patch. For example: What game is it(2,3,OA, ect.)? Is it a dedicated server? Have you port forwarded? Is there a Windows firewall exception or is it disabled? Is the router firewall enabled? Exception? Are you trying to host the server on windows? if so what Version? Is it the steam version of the game? What Mission is it? Windows Official: 1.62 is available from Arma 2 Official Web Site Beta: Newer builds are included in the ArmA II OA beta patches available here.