> If you know which build-dep likely caused the problem, we can make sure
> it's up-to-date and requeue opensp.
It appears there is a syntax error in /etc/xml/docbook-xml.xml (the XML
catalog for Docbook), so it cannot be parsed properly and therefore cannot
find a later entry for docbookx.dtd. The package docbook-xml creates this
file in its postinst with calls to update-xmlcatalog. I think if you purge the
docbook-xml package and then reinstall it, that might fix it. The purge will
remove the file completely and the reinstall will create a new file that
should have no errors. You might have to purge and reinstall again - if the
package that is there is old (which it appears it might be since it references
the ancient 3.1.7 version of Docbook), its postrm script might not handle this
correctly, but I see the latest package's postrm script does remove the file.
Can you do this and try the build again?