file upload error using php?

[Mittul Chuahan]

<?php
if(isset($_POST['submit_x']))
{
$file11 = $_POST['file11']['name'];
echo $file11;
}
?>
<form method="post" name="formproduct" id="formproduct" action="<?php $_SERVER['PHP_SELF'] ?>" enctype="multipart/form-data">
<input type="file" name="file11" id="file11" class="file_1" />
<br />
<input type="image" src="images/others/addnewproductblack.gif" name="submit" />
</form>

m using this php to fetch back file name which i have selected .. but m keep getting this error when i press submit image button ..

---------------------------------------------------------------
Notice: Undefined index: file11 in C:\wamp\www\product_touch_using_php\admin\try.php on line 4
---------------------------------------------------------------

please suggest me where m wrong