If you are trying to run an older version of Docmosis (eg v3) with a newer version of Libre Office (eg v5), then a simple configuration change is required.
Add the following lines to your settings (usually in your docmosis.properties file):
searchpath=[home]/program/classes;[home]/Basis/program/classes;[home]/URE/java;[home]/basis-link/program/classes;[home]/basis-link/ure-link/share/java;[home]/ure-link/share/java;[home]/ure/share/java;[home]/Resources/java
docmosis.openoffice.libraries. searchpath=[home]/basis-link/ ure-link/lib;[home]/ure-link/ lib;[home]/ure/bin;[home]/ program;[home]/Frameworks
docmosis.openoffice.libraries. list=uwinapi;sal3;libuno_sal. so.3;libuno_sal.dylib.3;jpipx; jpipe;libjpipe.jnilib
The Docmosis converter should then start happily.