fetching xml file, it has no line breaks = problem

I am fetching some xml files and parsing them using the built in
parser in php. Some of them work fine and i can extract what i need,
but some seem to return nothing, even when I know there is stuff in
there. Looking at the files, I have noticed that the ones that don't
work contain no line breaks. They are all fetched in the same way,
using

$merch = substr($key,1);
$feed = file_get_contents($_POST['data_url'.$merch]);
$fp = fopen("./feeds/feed".$merch.".txt","w+");
fwrite ($fp,$feed);
fclose ($fp);

, so it must be the way they are authored.

Would a lack of line breaks cause the parser any problems please ?