Webmaster Tools Microformats Error "Missing: updated" ?

Another blogging n00b question from me: I'm using WordPress to blog with and according to Google's Webmaster Tools every non-post page on the blog (categories, tags, page numbers etc) is "missing: updated" according to the structured data checking tool. Any easy way I can correct this? The blog posts themselves do no throw up this error but clearly everything else is. :/