[xml] xmllint - what does the error message "work/xslt/export_ifc.xml:2 : error: Content error in the external subset" mean?

["EXTERN Chakirov Timour (TZ CIS; DS/ESQ3)" <Timour Chakirov de bosch com>]

Hello All.

I'm trying to validate an .xml file against DTD using xmllint to this
manner:

------------------------%<----------------------
user:group> xmllint --dtdvalid
"file:///home/user/etc/xml/edc/filelist/1.0/dtd/export_ifc.dtd" --noout
work/xslt/export_ifc.xml
work/xslt/export_ifc.xml:2: error: Content error in the external subset
<!DOCTYPE FILE-LIST PUBLIC "-//EDC//filelist 1.0//EN" "">
^
work/xslt/export_ifc.xml:2: error: Extra content at the end of the document
<!DOCTYPE FILE-LIST PUBLIC "-//EDC//filelist 1.0//EN" "">
^
------------------------%<----------------------
What does these error messages mean? 

I'm asking because I always get these error messages, with any xml and dtd
files I'm trying to validate. And I got no error message if file export.ifc
contains no lines:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE FILE-LIST PUBLIC "-//EDC//filelist 1.0//EN" "">

And if I use this dtd in XMetaL to validate .xml-file everithing seems to be
ok too.

Could somebody shade lite upon this?

TIA,
Tim