headers sent error ! but they're not!

[OhLordy]

I'm getting a headers already sent error but they are quite obviously not. The page being displayed just has this error on it. It is sayong that the error is comming from an included file I have that looks like this.

<?

function cdwow_id($cdwow_id_array) {

sort($cdwow_id_array);
$part_one=substr($cdwow_id_array[count($cdwow_id_array)-1],0,4);
$part_two=substr($cdwow_id_array[count($cdwow_id_array)-1],4);
$part_two+=1;
if($part_two<10) {
	$part_two="00".$part_two;
} elseif($part_two<100) {
	$part_two="0".$part_two;
}

return $part_one.$part_two;
}
?>	

Can anyone think why this might be happening?
Thanks Rob

PS.
Here is the html being outputted by the oage if it helps

		<br />
<b>Warning</b>:  Cannot add header information - headers already sent by (output started at /home/httpd/maintenance/service/robert.y/woman/array.php:17) in <b>/home/httpd/maintenance/service/robert.y/woman/cosmetic/create_cosmetic_product.php</b> on line <b>35</b><br />

[PHPThorsten]

Maybe there is a space or a linebreak before or after the <?php ?> tags.

you should check this, they would cause that.

[OhLordy]

OK, I've now taken out ALL trailing spaces and spacer lines and I'm still getting an error. There are NO echos or prints in the array file or the file calling it so.

[PHPThorsten]

maybe you could post your code as zip file in here, so we can have a look on it.

[OhLordy]

My boss found the error. There was a sneaky little tab after one of the php close tags which I'd missed.
:o That'll teach me to be to hasy on my posting and check through my code before I do.
Cheers guys
Rob