It appears that the graphexample_data4.php file's header was written incorrectly. The first line of that file looks like this:
<?php echo "<" . "?xml version=\"1.0\" encoding=\"utf-8\" ?".">"; ?><?php echo "<" . "?xml version=\"1.0\" encoding=\"utf-8\" ?".">"; ?><!DOCTYPE wa_dwc SYSTEM "wa_dwc.dtd">
It should look like this:
<?php echo "<" . "?xml version=\"1.0\" encoding=\"utf-8\" ?".">"; ?><!DOCTYPE wa_dwc SYSTEM "wa_dwc.dtd">
Try replacing that first line in the graphs that aren't displaying correctly and see if that causes them to work.