Documentation can't be build off-line

Assembly sometimes fails. I suspect there is a DTD reference in the xml ( "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd" ), and since my system does not have direct access to the internet, it cannot download it.

[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4:53.988s
[INFO] Finished at: Fri Feb 11 14:57:53 CET 2011
[INFO] Final Memory: 26M/74M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal com.agilejava.docbkx:docbkx-maven-plugin:2.0.8-onms:generate-html (default) on project opennms-doc: Failed to transform userguide.xml. Failure reading /data/pguillebert_eclipse_ws/opennms/opennms-doc/src/docbkx/userguide.xml: Connection timed out -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException
[ERROR]
[ERROR] After correcting the problems, you can resume the build with the command
[ERROR] mvn <goals> -rf :opennms-doc
[ERROR] child exited with value 1