Hmmm I'm surprised no-one has spotted this before (or maybe they have)...but in category.html one of the tags is missing a %..

<%if meta_name%>
<meta name="description" content="<%meta_name%>">
<%endif%>
<if meta_keywords%>
<meta name="keywords" content="<%meta_keywords%>">
<%endif%>

Can you spot it ?