Deploy a plugin into the server. delete it ui is showing it as gone. upload that plugin again and see the following pop up in the UI (and server log) Failed to scan for updated plugins. [1322750254929] java.lang.Exception:File [/im/testing/jon-server-3.0.0.CR4/jbossas/server/default/deploy/rhq.ear/rhq-downloads/rhq-plugins/jopr-jboss-cache-plugin-4.2.0.JON300.CR4.jar] is not a valid jarfile - it is either corrupted or file has not been fully written yet. In fact the uploaded plugin is perfect and a valid jar file, but what happens is that the UI is by default not showing deleted plugin. The old version is still lingering around and thus preventing the deployment of the new one. Workaround is to click on "show deleted", then purge the old one and then re-try the upload.