It looks like you aren't passing the User_ID in the url when you update.
Instead you have it in a posted field.
You could probably just move the recordset code below the update code and fix the issue that way, since you redirect after update and the update code doesn't refer to the recordset.
Another way you can fix that by adding this line above the recordset (on line 57)
if (isset($_POST["WADAUpdateRecordID"])) $_GET['User_ID'] = $_POST["WADAUpdateRecordID"];
That way the User_ID parameter would be available, but really just moving it below makes the most sense because the code is more efficient. No need to create a recordset you aren't using.