I'm close but not close enough I'm afraid. And I've now run out of time as I'm going out. However this is where I'm at.
Change line 105 to
<td class="WADADataTableCell"><input type="text" name="date_name" id="date_name" value="<?php echo date('d/m/Y',strtotime($row_WADAdatetestTbl['event_date'])); ?>" size="32" /></td>
That will display the existing date in the format you like.
The thing that I'm not getting is how to convert that back so the MySql will accept it. The example that Jason gave does not seem to work when Updating a record.
How ever you do have an error in Line 55. You have the date set to d-m-Y and it should be Y-m-d which is the MySql way of writing it.
This is the line in full but it still updates with 000-00-00 so I'm stumped now and have no time to continue to play with it. Perhaps someone else will come to our rescue.
$WA_fieldValuesStr = "".((isset($_POST["event_date"]))?date("Y-m-d", strtotime($_POST["event_date"])):"") ."" . "|" . "".((isset($_POST["event_name"]))?$_POST["event_name"]:"") ."";
Incidentally you had the wrong field name in line 105. I think it was date_name instead of event_date so that was causing an error as well.