Seems to be caused by the new UI. Best guess would be it tries to popup some error/notice message that is not yet properly defined in the new UI.
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== C:\Program Files (x86)\Steam\steamapps\common\DayZ\DayZ.exe
== "C:\Program Files (x86)\Steam\steamapps\common\DayZ\DayZ.exe"
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Exe timestamp: 2015/02/24 14:42:05
Current time: 2015/02/25 16:49:23
Version 0.54.126645
"UI: <NULL-object> / <NULL-object>"