Out of curiosity are the errors in the "HTML Improvement Suggestions" or somewhere else? And what exactly are the errors? (The rest of this post is a guess you are seeing "duplicate" page messages).
If you change the category a product resides in after a search engine has indexed the site (or the search engine finds an old link on another website, your sitemap, etc) - this can happen.
I am not seeing a
<link rel="canonical" .. /> in the head section of your page. I believe 1.3.9h adds this by default unless it is disabled by the theme. Having this tag should solve the issue.
If you are against using a canonical tag, you can manually create 301's from the incorrect location to the correct location. A bit more work, but also would solve the issue.