Woops I can't parse your feed
validator.w3.org
try just removing:
# <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
# <html xmlns="http://www.w3.org/1999/xhtml">
and see if it validates