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.

Oh thank you, thank you, thank you! It worked, it worked, it worked!!!! I've been working on this for ages! I can't tell you how grateful I am!
Marc

No problems mate.
Just beware of SED saving as WDL by default, and that if you
have a *.WDL of the same name as you *.c it will auto-include.

They still bite me on a regular basis....

Enjoy

um..well
cough! cough!

I copy and pasted your program Marc in the Lite C
script ediotr and it wouldn't compiler due to some errors. After about 10 minutes or so going thru the whole program...I noticed there was no closing bracket for the function main.
So, I added a closing bracket and the program compiled and ran.

Here is the modified program:

////////////////////////////////////////////////////////////////////
#include <acknex.h>
#include <default.c>

var a = 7;
var b = 10;
var c = 0;

/////////////////////////////////////////////////////////////////////

PANEL* panDisplay =
{
digits(35, 10, "a = %0.f", *, 1, a);
digits(35, 19, "b = %0.f", *, 1, b);
digits(35, 28, "c = %0.f", *, 1, c);
flags = VISIBLE;
}

/////////////////////////////////////////////////////////////////////

function main()
{
video_mode = 7; // create a program window of 800x600 pixels
screen_color.blue = 150; // and make its background dark blue
while (1)
{
c = a + b;
wait (1);
}

}

its cool to style and indent your code.
If you want and like.

When I save as, I all ways type the .c after the name of the file.