Ben bir hata almaya devam: Notice: Undefined index: satırında 35

hat 35:

 $handle = new Upload($_FILES['my_field']);

Bu benim giriş alanıdır

 <input type="file" size="32" name="my_field" value="" />

Ben bu hatayı anlamıyorum, teşekkürler!

EDIT:

 <form name="upload" id="upload" enctype="multipart/form-data" method="post" action="actions/upload.php" />
 <p><input type="file" size="32" name="my_field" value="" /></p>
 <p class="button"><input type="hidden" name="action" value="image" />
 <br>
 <input style="margin-left:224px;" type="submit" name="submit" value="upload" />