What the heck is this DocBook error?

I DocBookified the TWIG manual, but I can't compile it due to some strange errors that don't appear to be coming from the DTD...

jade -t tex -V tex-backend
-d print.dsl
/usr/share/sgml/xml.dcl AdminManual.db
jade:AdminManual.db:3:57:E: URL not supported by this version
jade:print.dsl:1:0:E: end of document in prolog
jade:E: specification document does not have the DSSSL architecture as a base architecture
make: *** [AdminManual.tex] Error 1