Hoople - 1:07 am on Dec 14, 2011 (gmt 0)
Segment the page into multiple TEXT files leaving the ending /body and /html tags in place. Work through the first one fixing the validation issue. Then add them back one at a time and repeat. After 20+ years doing HTML I end up doing this once a year or so. It creates a real 'face-palm moment' when you find it too!
There are a number of online HTML validators (<--- good search term). Sometimes these validator error reports are decidedly UN helpful. Comparison validation checks may find the one little thing that causes tens of errors to be reported.
Oh....by the way....welcome to WebmasterWorld justint!