<a class="goods-image-medium-square" id="mainImage" itemprop="caption" itemprop="image" href="{goods_images.LARGE}" data-fancybox="gallery" target="_blank" title="{GOODS_NAME}"> {%IF goods_images.index = 1%}<img class="goods-image-medium" src="{goods_images.MEDIUM}" alt="{goods_images.NAME}" />{%ENDIF%}
замените на:
<a class="goods-image-medium-square" id="mainImage" itemprop="image" href="{GOODS_IMAGE_MEDIUM}" data-fancybox="gallery" target="_blank" title="{GOODS_NAME}"> {%IF goods_images.index = 1%}<img class="goods-image-medium" src="{GOODS_IMAGE_MEDIUM}" alt="{goods_images.NAME}" />{%ENDIF%}