Hey there!
So, from beginning. As first time i tested exp0.6 i could not open steam overlay (shift+tab). Did not have this problem on 0.59 until 0.6 stable came out. Tryed configure new keybind, uninstalled fraps, turned off win essentials, deleted steam userdata folder, verifyed game files. Dont use any launch parameters, any recording program. Overlay works on other games as usual. And there is no GameOverlayUI.exe in task manager when dayz.exe running. Have latest NVIDIA drivers. Gforce GT555M ver.368.39; intel i5 2430 cpu. I hope i gave as much info as You need. Keep the good work!