can't install libsecret

make[3]: Entering directory `/usr/ports/contrib/libsecret/work/src/libsecret-0.15/docs/man'
  GEN      secret-tool.1
I/O error : Attempt to load network entity http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl
warning: failed to load external entity "http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl"
cannot parse http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl
make[3]: *** [secret-tool.1] Error 4
make[3]: Leaving directory `/usr/ports/contrib/libsecret/work/src/libsecret-0.15/docs/man'
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory `/usr/ports/contrib/libsecret/work/src/libsecret-0.15/docs'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/usr/ports/contrib/libsecret/work/src/libsecret-0.15'
make: *** [all] Error 2
=======> ERROR: Building '/usr/ports/contrib/libsecret/libsecret#0.15-1.pkg.tar.gz' failed.
prt-get: error while install

-- Packages where install failed
libsecret