Question

I am trying to validate an xhtml strict document with a linked css and I keep 
getting a large error screen.  The document validates fine in HTML 4.01 
strict.
Is there something I have forgotten?  
The url is http://www.people.fas.harvard.edu/~balling/kb2/partb.html.
Please let me know if there is something wrong with the validation tool or if 
it clearly my code.
Thanks a million.