Notice in the error log that it says the error is in ATEST.WDL.
That means that your file has (at least once) been saved as a *.WDL file instead of the required *.C file.
The script editor is a bit awkward this way. The fix is this simple.

In SED, click FILE / SAVE.AS and when the dialog comes up,
type in ATEST.C and hit enter. Its now SAVED correctly.

NEXT you will need to use windows to go the folder where it lives and delete the *.WDL version of ATEST.
(Annoying note: If there exists a *.wdl that matches its name to your *.c file,
it will automatically be included and usually causes errors)

Then try running your *.c file again and it should work.