This is how you fix it. I tried everything you listed, but once i did this it finally worked. Go to steamapps in the steam folder and move it to your desktop(might take awhile depending on how many games you have installed). Then once it's on your desktop, move dayz out of the common folder in steamapps and delete it. Make sure the steamapps is still on your desktop and uninstall steam. Once you have steam uninstalled, install a new version of steam from the steam website. Once the new version of steam is installed, go to the new steamapps folder in the steam directory and move everything from the old steamapps folder on your desktop to the new steamapps folder. Once you did that, install dayz again and it should work. This guy also tried it and it worked, here is his post http://feedback.dayzgame.com/view.php?id=19656&nbn=3#bugnotes

Hello phelsan,

To begin with I would recommend that you try to verify the integrity of the game cache:

1. Start Steam and right click on DayZ in your game library (make sure that the game is not running).
2. Select the tab labeled "Local Files".
3. Click on the button labeled "Verify integrity of game cache...".
4. Start DayZ once the process is complete.

In case this does not solve your problem either, I can have a look at your account in the character database if you send me a link for your Steam Profile ID.

Regards,
JStewart

Hello again,

Closing ticket due to inactivity. However, in case the problem persists, please feel free to open up a new ticket in the Feedback Tracker.

Regards,
JStewart