According to the wiki the Serena Deploy Plugin requires several jars to be installed in the WEB-INF/lib directory of the Jenkins war.

This is a bug because it pollutes the classloader of all Jenkins plugins, which can result in anomalous or buggy behavior. Instead, required libraries should be bundled with the plugin in its own WEB-INF/lib. If this is not possible due to licensing restrictions, the user should be able to upload the files or provide an alternate path to where the plugin can load the dependencies from