ERRNO just means an error with the window definition. There is no info what the particular numbers mean.

The starter window compiler was written 15 years ago, that's why its error display might be not really state of the art today. On the other hand, the possibility to make errors in a starter window definition is somewhat limited. When the error is independent of the content, then you likely won't solve it by fixing the content - something else is wrong, for instance compiling the wrong file.

You can call the starter window compiler, wdfc.exe, also directly from the command line (assuming your starter window definition is "mystart.wdl"):

wdfc -smystart.wdl -omystart.wdf -t -ex -run