Why are my form variables not getting found?

<?
include($_SERVER['DOCUMENT_ROOT'] . '/upload/class.upload_27.php');

$dir_dest = $_SERVER['DOCUMENT_ROOT'] . "/otheruploads/";

$files = array();
    foreach ($_FILES['my_field'] as $k => $l) {
        foreach ($l as $i => $v) {
            if (!array_key_exists($i, $files))
                $files[$i] = array();
            $files[$i][$k] = $v;
        }
    }


foreach ($files as $file) {

        // we instanciate the class for each element of $file
        $handle = new Upload($file);

        // then we check if the file has been uploaded properly
        // in its *temporary* location in the server (often, it is /tmp)
        if ($handle->uploaded) {

            // now, we start the upload 'process'. That is, to copy the uploaded file
            // from its temporary location to the wanted location
            // It could be something like $handle->Process('/home/www/my_uploads/');
            $handle->Process($dir_dest);

            // we check if everything went OK
            if ($handle->processed) {
                // everything was fine !
                echo '<fieldset>';
                echo '  <legend>file uploaded with success</legend>';
                echo '  ' . round(filesize($handle->file_dst_pathname)/256)/4 . 'KB';
                echo '  link to the file just uploaded: <a >file_dst_name . '">' . $handle->file_dst_name . '</a>';
                echo '</fieldset>';
            } else {
                // one error occured
                echo '<fieldset>';
                echo '  <legend>file not uploaded to the wanted location</legend>';
                echo '  Error: ' . $handle->error . '';
                echo '</fieldset>';
            }

        } else {
            // if we're here, the upload file failed for some reasons
            // i.e. the server didn't receive the file
            echo '<fieldset>';
            echo '  <legend>file not uploaded on the server</legend>';
            echo '  Error: ' . $handle->error . '';
            echo '</fieldset>';
        }
    }
?>

Notice: Undefined index: my_field in /home/mydir/system/core/core.functions.php(637) : eval()'d code on line 7

Warning: Invalid argument supplied for foreach() in /home/mydir/system/core/core.functions.php(637) : eval()'d code on line 7

<form name="form3" enctype="multipart/form-data" method="post" action="/actions/doupload">
            <input type="file" size="32" name="my_field[]" value="" /></p>
            <input type="file" size="32" name="my_field[]" value="" /></p>
            <input type="file" size="32" name="my_field[]" value="" /></p>
            <input type="submit" name="Submit" value="upload" /></p>
        </form>