Sorry for the delay with the reply.
> External resource loader: CustomFileResourceProvider not found. Make sure “pd4ml.extra.resource.loaders” value is correct
Obviously the classloader cannot find CustomFileResourceProvider class (which is expected to be in the classpath)
Well, your idea to add the class to the pd4ml_demo.jar is not that bad. But before you re-packed the JAR and deployed it to the Domino environment, try to debug CustomFileResourceProvider offline. You may run PD4ML in GUI mode:
java -Xmx512m -cp .;pd4ml_demo.jar;ss_css2.jar -Dpd4ml.extra.resource.loaders=CustomFileResourceProvider org.zefer.pd4ml.tools.PD4Browser
(The application will auto-create pd4browser.properties. In the file you may set debug.info.enable=true to allow the debug output)
You would also need to add to the classpath the specific domino SSL lib(s)