fresh install over iis, + GD library.

my script:
<?
header ("Content-type: image/png");

// image size is 529x656 and its a map.
$img=imagecreatefrompng ("image.png");

for($i=0;$i<5;$i++)
{
	$x=rand(0,imagesx($img));
	$y=rand(0,imagesy($img));
	imagefill ($img,$x,$y,0x9f23a4);
	
}

imagepng ($img); 
imagedestroy($img);
?>

this results in:
"
CGI Error
The specified CGI application misbehaved by not returning a complete set of HTTP headers. The headers it did return are:
"

nothing more...