I'm having the same problem here.
Using the latest C2 with the latest NWjs4C2.
I click on "preview" and nothing happens but a process called "nw.exe"
is started in the Task Manager and gets there until I manually kill it.
Also, "Letterbox Integer Scale" doesn't work anymore for me and it's just regular size.
I was trying to create a new example but failed to reproduce the first error as all of them worked.
The scale problem works with every project, new or old.
I use Ajax, Sprites and Texts in my project with the Tween behaviour.
All of them work separately in a new project. :-/
Same setup and versions of the OP.