PHP not being executed when user is anonymous

I started a thread elsewhere, but realized I should put this here. http://drupal.org/node/1783732

I have noticed that when I am not an authenticated user, the php code is not being executed. To test that this is the case, I am writing to a temp file. As an authenticated user, the file is written to... When I view the site without being logged in, the file is not written to.

Any thoughts?

Here is my code:

// set node id
$nid = $row->field_ss_slide;

// create an array to store node ids
$nids = array();

// populate node ids
$nids[] = $data->nid;

// open a temp file to test if code is being executed
$fh=fopen('/tmp/anon','a');
fwrite($fh, "works");
fclose($fh);

// get list of image files from the database
$result = db_query("SELECT field_ss_slide_fid FROM {field_data_field_ss_slide} WHERE entity_id = :nid", array(':nid' => $nid));

// loop through the list
foreach($result as $record){
    // grab uri of individual image
    $file = db_query("SELECT uri FROM {file_managed} WHERE fid= :fid", array(':fid' => $record->field_ss_slide_fid ));
    $x=0;
    
        // store uris
    foreach($file as $filename){
        $uri = $filename->uri;
        $uris[$nid][] = $filename->uri;
        
        $x++;
    }

}

$cnt = count($uris[$nid]);
$num = rand(0, $cnt-1);
$uri = $uris[$nid][$num];
$file = file_create_url($uri);