Twenty Twelve Custom Post Image

Hi all,

I am building a child theme off the Twenty Twelve default theme, and having an issue displaying my custom image size, I had previously had this code working on a basic theme I put together from scratch but no joy getting it to work properly so far.

The current result that is displayed can be found here

https://coder-tronics.com/articles-2/

I have a fair bit of code for the custom post type which for the most part seems to be working, in the back administration panel, the code for the custom image size in the functions.php file is below:

/* CUSTOM POST THUMBNAILS --------*/
if ( function_exists( 'add_theme_support' ) ) {
	add_theme_support('post-thumbnails');
	add_image_size('custom-portfoliothumb', 320, 120);
}</strong>

And I am using this on a custom page template in this way:

<strong>			<div id="portfolio-item">
				<h2><?php the_title(); ?></h2>
				<a>"><?php the_post_thumbnail('custom-portfoliothumb');?> </a>
				<?php the_excerpt(); ?>
			</div>

[Please post code & markup between backticks or use the code button. Your posted code may now have been permanently damaged by the forum’s parser.]

Obviously I am doing something wrong but not quite sure yet, hence the question. I have tried looking at the result in firebug but no clues as yet, as I said the code did work in basic theme, so I believe the code is not interacting with Twenty Twelve as it should. Fairly new to the child theme idea and Twenty Twelve.

I can post more code if required but didn’t want to place too long a post.

Cheers,

Ant