Hello,
in Steam Library, please right-click on Arma, set Properties, tab "Updates" and change it to "Always keep this game up to date".
Does it help?

Hello, yes since I bought it.Ever "Always keep this game up to date".

There was many WLA players with similar issue. They solved it by right clicking arma3 in steam -> properties -> verify local files. That make it redownload possible corrupted files which prevented the update for some reason.

SaOk, I ve verified local files and it founded some problems with it. Now start the update message, but rest to 0%, and at last show this message window: Steam - Error There was an error while updating Arma 3 (connection timed out).

Try to check if you are blocking any ports:

http://support.steampowered.com/kb_article.php?ref=8571-GLVN-8711

Hello Killzone Kid,

I've other steam games, and update work. Just now "Rust" is updating.