Why is my PHP script returning different results on similar inputs?

Background: I am doing ajax calls to a PHP script which returns data to fill a form based on some file key a user inputs. This form is used so users may edit an incorrectly inputted file key from their original submission.

Problem: If a user wanted to edit a file key, they input it into a text box, hit a button for an ajax pull, the form fills, they can then correct their mistakes and submit. However, if they try to edit the new file key again, the form will not fill and I am getting no results returned from the query. This is the php script I have been using to pull the data from the server.

A sample file key might be: 10000010000-0D-MAN.

This is a good response: 10000010000-0D-MAN,N/A,amibaguest,dfgfdgfd,Electrical

This is the response I get on a newly edited file key: Nothing returned. Id: 20000010000-0D-MAN

Really baffled at the moment. If more information is needed, please let me know.

$dbhandle = mysql_connect($hostname, $username, $password)
    or die("Unable to connect to MySQL");

$selected = mysql_select_db("database", $dbhandle)
    or die("Could not select database");

$id = $_GET['param'];
if(isset($_GET['param'])) {
    $sql = sprintf("SELECT a.File_key, a.Name, a.Uploader, a.File_descriptor, b.keyword1 FROM files as a, keyword as b WHERE a.File_key='%s' AND a.File_key=b.File_key", mysql_real_escape_string($id));
    $result = mysql_query($sql);
    if($result === FALSE) {
            echo mysql_error();
    }
    if(mysql_num_rows($result)==1) {
            while($myrow = mysql_fetch_array($result)) {
                    $file_key = $myrow["File_key"];
                    $name = $myrow["Name"];
                    $uploader = $myrow["Uploader"];
                    $file_desc = $myrow["File_descriptor"];
                    $keyword = $myrow["keyword1"];
                    $text_out .=  $file_key.",".$name.",".$uploader.",".$file_desc.",".$keyword;
            }// end while
    } else {
            $text_out = " Nothing returned. Id: ".$id;
    }// end else    
}// endif
echo $text_out;