Some images only showing alt text in Firefox but load fine in Safari or Chrome yet other images on the same page load fine

I'm making a simple website for myself using wordpress and some hacking to try and teach myself a little about web coding for fun. I've set up my website and http://jonhocking.co.uk and I'm using a series of 4 squares on the front page to navigate around the site. Three of these link to categories and these images display perfectly fine. The other links to a wordpress page and although I've used the same code, it's only showing the alt text for the image. This bug only happens when using Firefox. I've tested it with Chrome and Safari which both show the page as expected and I haven't tested it with IE since I'm using OS X and haven't had the chance to. The same problem occurs with the logo in the top left corner. This logo links to the main page and only shows the alt text in firefox. I have also tried using mobile Safari on the iPhone and this has the same problem.

The code for the main index:

<?php get_header(); ?>
<div class="main_link">

<a href= "http://jonhocking.co.uk/?cat=3"><img src="<?php bloginfo('template_directory'); ?>/images/Current.png" /></a>

<a href= "http://jonhocking.co.uk/?cat=4"><img src="<?php bloginfo('template_directory'); ?>/images/Previous.png" /></a>

<a href= "http://jonhocking.co.uk/?cat=1" ><img src="<?php bloginfo('template_directory'); ?>/images/Blog.png" /></a>

<a href= "http://jonhocking.co.uk/?page_id=85"><img src="<?php bloginfo('template_directory'); ?>/images/BlogRoll.png" alt = "Blog-Roll"/></a>

</div>


<?php get_sidebar(); ?>
<?php get_footer(); ?>

The only difference is the addition of alt text to the Blog-Roll image so I can at least see something loading in FF and also the fact that Blog-Roll is a page not a category. Have I missed out something obvious 开发者_如何学编程here?

Thanks,

Jon

---

The blogroll.png image is not appearing for me in any browers - I just checked safari and chrome. Perhaps you have it cached in those browsers and removed it from the server accidently.

Accessed it directly with http://jonhocking.co.uk/wp-content/themes/UpstartBloggerModicus2c/images/BlogRoll.png also - this image does not exist or is corrupt.

---

Firefox says, The image “http://jonhocking.co.uk/wp-content/themes/UpstartBloggerModicus2c/images/BlogRoll.png” cannot be displayed, because it contains errors..