Like I said I had no problems for last 10 days. It started suddenly few hours ago (before that I was using nodewebkit preview all the time). Since then it's permanent for every opened/created project.
At first when it happened I was exporting my project to exe and my antivirus soft gave me a popup notification about "potentially dangerous file" and delete exe from exported folder. It was kind of strange but i've added C2 folder and folder for export to exclusions and then exported my project without any problems. And since then node webkit don't work for me at all. Got same window like sqiddster on preview, and no exe file after export - even while antivirus soft is completely turned off.
sqiddster does it work fine for you after exporting?