It appears there has been a game breaking update to arma3 that has not been rolled back, so for the time being alot of you will need to sit and wait for their hotfix, more info here: https://forums.bohemia.net/forums/topic/220618-update-186-verify-signatures/?page=2&tab=comments#comment-3327107
We apologise for this inconvenience and will update you as and when we know more.
update 1: Weve added a Legacy 184 Roll back steam button in your gamecp to roll back to a previous version of arma3 if you dont want to wait for the hotfix
update 2. It appears that only one 1.86 server can run/start on any single machine, all subsequent servers then attempting to run will all fail to start, only being able to start when using legacy branch (we strongly advise all clients to wait for the hotfix)
Update 3. Weve changed the rollback steam update button to a release candidate 1.86.145242 for people to get servers back online if anyone is having issues we request you test/try this from your game panel (any servers failing to update properly stop the server, in your filemanager delete the "steamapps" folder, then re-run the 1.86 roll back steam update) (legacy branch 1.84 is still the only confirmed working fix)
Update 4. Roll back updates removed as an option from game panels, todays hotfix confirmed working for all servers Hotfix v1.88.145263 (Multiplayer Compatibility Fixes), we recommend deleting steamapps folder in your root directory then run a steam update from your game panel, anyones server still failing to start we recommend you remove all mods and re-add one by one to find any that needs fixing due to this update or wait for MOD authors to supply fixes, please submit a ticket if youre still unsure. https://dev.arma3.com/post/spotrep-00083
Tuesday, December 4, 2018