Hi,
recently many updates were made as a follow-up of WordPress 3.x. I'm assuming you've updated WordPress recently. To solve the issue you have to update the WooCommerce plugin and the Propulsion theme. You can download the latest version of Propulsion though ThemeForest(free of charge) in your "downloads" section.
Some image sizes are defined in the functions.php, see:
$avia_config['imgSize']['widget'] = array('width'=>36, 'height'=>36 ); // small preview pics eg sidebar news
$avia_config['imgSize']['post-format-image'] = array('width'=>630, 'height'=>999, 'crop'=>false); // big images for post format image and gallery posts
$avia_config['imgSize']['fullsize'] = array('width'=>930, 'height'=>930, 'crop'=>false); // big images for lightbox and portfolio single entries
$avia_config['imgSize']['featured'] = array('width'=>930, 'height'=>340); // images for fullsize pages and fullsize slider
$avia_config['imgSize']['portfolio'] = array('width'=>450, 'height'=>335); // images for portfolio entries (2,3,4 column)
//dynamic columns
$avia_config['imgSize']['dynamic_1'] = array('width'=>446, 'height'=>151); // images for 2/4 (aka 1/2) dynamic portfolio columns when using 3 columns
$avia_config['imgSize']['dynamic_2'] = array('width'=>609, 'height'=>210); // images for 2/3 dynamic portfolio columns
$avia_config['imgSize']['dynamic_3'] = array('width'=>688, 'height'=>151); // images for 3/4 dynamic portfolio columns