XHTML DTD doesn't validate?

[ Please CC any replies to me as I'm not on the www-validator list. ]

Hiya - I have some pages that I've been converting to XHTML;  they pass the
W3C's validator at:

  http://validator.w3.org/

as XHTML, but when I run them through the XML validator at:

  http://www.stg.brown.edu/service/xmlvalid/

(to double-check anything I or the W3C validator have missed) I'm surprised
that my documents can't be checked because the XHTML DTD causes a whole heap
of warnings and errors, such as:

  line 38, http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd:
    error (771): malformed external parameter entity;
    file: http://www.w3.org/TR/xhtml1/DTD/xhtml-special.ent, line 29

Of course, it makes it a tad difficult to ensure that I've got everything
"just right" when the XHTML DTD itself won't validate.  :-(

Is it the XML validator that's broken or the DTD?  Is this "normal" for the
XHTML DTD, or is there some way it could be rectified?

Thanks..


dave