your file names are using a variable from a recordset:
$row_DLA_Event['ID'] ."img1"
The DLA_Event recordset is set to filter on a querystring variable that is not passed when the form submits:
<form action="" method="post" enctype="multipart/form-data" class="middle-forms" id="add_media">
I think the main cause of the issue is that the images are not being properly to begin with.
change the forms action to:
action="<?php echo $_SERVER["PHP_SELF"]; ?><?php echo (isset($_SERVER["QUERY_STRING"]) && $_SERVER["QUERY_STRING"] != "")?"?".$_SERVER["QUERY_STRING"]:""; ?>"
this will make sure any querystring variables that are passed in get passed along with the form submission.