two days ago, I was able to play DayZ, but today steam comes up with in the headline mentioned message.
Did all steps described in here:
https://support.steampowered.com/kb_article.php?ref=8676-EFLX-7453&l=english&steamid=76561198025096282&errortype=EAppUpdateError&errorvalue=28
As well re-installed the game completely.