A simplified version of your code works, which suggests the problem is elsewhere on the page.
<div itemscope itemtype="http://schema.org/Product">
<h2 class="product_name" itemprop="name"><span>Bengali</span></h2>
<div itemprop="aggregateRating" itemscope itemtype="http://schema.org/AggregateRating">
<meta content="50" itemprop="ratingValue" />
<meta content="100" itemprop="reviewCount" />
<meta content="100" itemprop="bestRating" />
<meta content="0" itemprop="worstRating" />
So we can at least eliminate problems with the ratings code itself. I've tried a number of things to pin down what it is, including but no luck so far.
I think you need to go through a process of elimination with the entire page code to find out what's causing this.
Some possibilities I've explored:
- The ratings code comes above the actual product info in the code. When I replicate that with my simplified version of your code, by moving the product name beneath the review, I get an error. There's no such error with your full page code, but nevertheless I wonder if there may be some issue there.
- Google's page on these Rich Snippets suggests using only one type of review markup on a page. I did try removing your individual reviews without success, but again, something to consider in combination with other things.