by default DW does not use asset() which it should for GET variables.
in the show region behavior, when you select a URL Variable binding, the code will look like:
<?php echo $_GET['error']; ?>
you should change that to use asset to prevent undefined index errors if the URRL variable is not set:
<?php echo(isset($_GET['error'])?$_GET['error']:""); ?>
this is a limitation to the DW Bindings panel.