PHPthumb unknown image type

I recently moved a site running Treasurechest.

The site all works fine apart from the main product image. if i hover over the image I get an ajax pop-up as I should, but the image itself is replaced by the following error:



The page is here;

http://79.170.40.234/gollygaloshes.com/index.php?q=pony

Can you use .png files with phpThumb ?

I have been using it successfully on that site before, its only since the move.

I imagine some config file needs updating or something but I don’t know where to start

The exact error message is: