you dont have understand the syntax. you cant create a window with just saying FULLSCREEN
Syntax:
static Window* Create(const std::string& title="Leadwerks", int x=0, int y=0, int width=1024, int height=768, int style=Titlebar)
--Create a window fullscreen
self.window=Window:Create(title, x, y, w, h, Window.FullScreen)
like HD
self.window=Window:Create('MYWINDOW', 0, 0, 1920, 1080, Window.FullScreen)
parameters can also be variables. which type you can see in the syntax description