Firstly: I'm a lowly web designer who knows just enough PHP to be dangerous and just enough about server administration to be, well, nothing. I probably won't understand you unless you're very clear!

The setup: I've set up a website where the client uploads files to a specific directory, and those files are made available, through php, for download by users. The files are generally executable files over 50MB. The client does not want them zipped, as they feel their users aren't savvy enough to unzip them. I'm using the php below to force a download dialogue box and hide the directory where the files are located.

It's Linux server, if that makes a difference.

The problem: There is a certain file that becomes corrupt after the user tries to download it. It is an executable file, but when it's clicked on, a blank DOS window opens up. The original file, prior to download opens perfectly. There are several other similar files that go through the same exact download procedure, and all of those work just fine.

Things I've tried: I've tried uploading the file zipped, then unzipping it on the server to make sure it wasn't becoming corrupt during upload, and no luck.
I've also compared the binary code of the original file to the downloaded file that doesn't work, and their exactly the same (so the php isn't accidentally inserting anything extra into the file).

Could it be an issue with the headers in my downloadFile function? I really am not sure how to troubleshoot this one…

This is the download php, if it's relevant ($filenamereplace is defined elsewhere):

downloadFile("../DOWNLOADS/files/$filenamereplace","$filenamereplace");

function downloadFile($file,$filename){    
    if(file_exists($file)) {
        header('Content-Description: File Transfer');
        header('Content-Type: application/octet-stream');
        header('Content-Disposition: attachment; filename="'.$filename.'"');
        header('Content-Transfer-Encoding: binary');
        header('Expires: 0');
        header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
        header('Pragma: public');
        header('Content-Length: ' . filesize($file));
        @ flush();
        readfile($file);
        exit;
    }
}