5o6

Yeah I know this is an old thread but here's the solution because no one else wants to post it and this is the first link that comes up when you google this issue. You need to go to the arma3server.cfg file in your server files and remove -autoInit from the server start parameters. (On my install it was enabled by default, might be a linuxgsm thing.) You can only edit the mission parameters so long as the mission hasn't started, and autoInit automatically starts the mission as soon as it is loaded. This is why you can sometimes edit the mission parameters, because you happen to click the parameters button faster than the server can load the mission. Also yes you have to be logged in as admin to edit mission parameters.