I had an invalid date error with epubcheck. I went ahead and did the edit in an TextEdit and fixed the date. Now it passes the epubcheck just fine but my table of contents has gone missing.
Why would that happen since I only changed the date inside the Metadate.opf?
Changed to <dc:date>2011-10</dc:date
Very confusing. Before I fixed the epubcheck date error, I could get the full TOC when opening the epub file in Adobe Digital Editions.