I have experienced the same error. Until now, it always happened to the host. Even after we played some hours without problems, it occured after a restart.

Same issue for me, and I can't close out of Arma without bringing up either the task-manager or alt-f4'ing it. It seems utterly random, which makes it worse.

Alright, so, not sure if this will work for y'all - but this is 10:10 success for me. After extensive fiddling and ad hoc ♥♥♥♥♥♥♥♥...

When you start the game, and it pulls up the map for the first time with the "Continue" button, do not press it. Wait until everything on map (markers, terrain and bases and such) have been generated, and the "Tasks" tab to enter the scenario window. That part I've found weirdly crucial.

If Tasks pops up before everything else is generated, it will trap you in the map as per the problem. Hit "back" and restart the scenario. If everything generates and *then* "Tasks" pops up, it should work. That's what I've stuck to, and I've found it a flawless workaround. Tedious, a bit - but it's yet to fail me. Hope it helps.