downloading an application from a site

[infernodeep]

hi
can anyone help me plzz im very new to php.

http://localhost/cion_latest/download.php?code=adm&user=7&download_type=trial

from this im try to download an application.
Application downloading correctly but when im try to install app. im getting this error

This installation package could not be opened.
contact the application vendor to verify that this is a valid windows installer package.

but in original app. works fine

this is im sending

$query_string = 'code='.urlencode($_POST['pname']).'&user='.urlencode($row[id]).'&download_type=trial';
<a href="http://localhost/cion_latest/download.php?'.htmlentities($query_string).'">http://localhost/cion_latest/download.php?'.htmlentities($query_string).'</a>

im attaching the code also
plz.. its very urgent