The newest version of xmlto (0.0.23) attemps to validate all documents through open network connection. This affects all Cygwin source builds. The symptoms:
I/O error : Attempt to load network entity http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl ... SOLUTION If you're having promlems under Cygwin, modify the makefiles to use: xmlto --skip-validation ... Jari Further reading: - There is discussion about the issue in <https://trac.macports.org/ticket/26151> which point to a patch like <https://trac.macports.org/attachment/ticket/26151/26151.diff> where adding an additional option in call to xmlto makes it work with latest version. - xmlto author's project page http://cyberelk.net/tim/software/xmlto/ reads: Attempt to load network entity ... failed to load external entity This is caused by the absence of correctly configured XML Catalogs on your system. When XML Catalogs are available, URLs are transformed into local file references. In particular, Debian does not provide XML Catalogs. For more information about XML Catalogs see the xsltproc documentation <http://xmlsoft.org/catalog.html>.