Invalid XHTML

I’m sorry if this is a stupid question, but I just tried to validate my XHTML and it came up with 22 errors. None of these are too threatening (some extra </p> and </div> tags, etc.) but I would like to resolve them anyhow. The only problem is, I can’t find the source page.

My blog address is http://blog.groundworkopportunities.org but I’m not sure which page it is re-routing me to that has the XHTML errors (especially since everything is php). Could someone please let me know which file I need to look in to fix these errors.

Thanks.