Well, I ran my 3.2 version across W3C and this error was thrown:
"The itemprop attribute was specified, but the element is not a property of any item."
I searched the web and looked at the code and the problem relied on the Product Review Stars.
You can take a look at ProductReviewOverview.cshtml
Anyways, the FIX was easy, just:
1) Open _Root.Head.cshtml
and change the BODY tag and leave it like:
<body class="@colorPreset @texture" itemscope itemtype="http://schema.org/WebPage">
That's it. Im using a theme, but I believe this problem is also on the default theme.
If it its, you should include it.
Hope it helps.
Regards