The first error is because you added this to the top of the page:
<!--Codigo_nuevo-->
HTML comments need to be in the html... to do a php comment use:
php:
<?php //Codigo_nuevo ?>
You also can't have blank lines before a redirect in php. So make sure to remove the blank lines on lines: 15,40 and 59 and update the other HTML comments above the <html> tag to use php comments instead.
I'd also remove the line:
php:
<?php
ob_start();
?>
The validation isn't working because you used the Binding for "file extension"... it is a bit confusing I know, but you should use "client file name". The validation looks for the "." before the extension to validate against and the "file extension" binding removes the ".".
Did this help? Tips are appreciated...
