When I try that it gives me "Error has occurred: ERRNO #288.289", exactly the same as from the commandline with WED. I have tried
as the content of the file main.wdl and the command line was
C:\Users\My User Name\Desktop\test>"D:\Program Files (x86)\GStudio8\wdfc" -smain.wdl -omain.wdf -t -ex -run
I can confirm the same error message if I use code above, but you need use as minimum MODE STANDARD; see below and you are fine.
WINDOW WINSTART
{
MODE STANDARD; // always required
}
from the manual:
MODE style;
The window mode (always required within the WINDOW definition) . Style can be either STANDARD, IMAGE, FULLSCREEN, or USE_OLDSTYLE.