Norcath

I have exactly the same issue. It began on May 29th with Steam endlessly trying to update itself, then applying the same Game updates over & over (Approx 11 Games incl. DayZ were affected). If the updates were allowed to complete & the game selected for play the above error would appear; any attempt to close & retry would result in a "Game is already running Error" I contacted Steam & after almost a week of troubleshooting & multiple emails we managed to resolve the Steam Update Error. This also resolved 'some' of the Game Update misques (Primarily Valve Titles), but unfortunately DayZ was not among them. I was notified I'd have to contact each Developer individually. This has been a rather 'painful experience'. However, I'm pleased to say after much trouble shooting (usually revolving around Direct X/ Reinstallation of Game Files) Civ 5 & it's add-ons work & we're 90% sure we have a solution fo StarTrek: Online:).. I'm mentioning the above to illustrate that the problem appears to be focused on the Steam Update, is far from isolated to DayZ, & to clarify all of the 'quick' fixes have been tried. IE. Reinstall the Game Client, Steam, Run as Admin, verify Cache, etc. Any ideas or suggestions would be greatly appreciated, currently the game is non-functional, thx.