After upgrading the IPMI firmware, the console redirection JAVA applet can be loaded successfully. However it just shows a black screen where the title bar says “Java iKVM Viewer v1.69.24 - No Signal”, no matter if I use Mac or Windows machines. We did iKVM reset, and the video feed is working properly after iKVM reset. But it's strange that on one of the machines, the keyboard is not functioning after the reset.
Answer
Try to clear Java cache in Java Control Panel. Go to General => Settings => Delete Files to delete the temporary files. Detailed instruction can be found on Java website: http://www.java.com/en/download/help/plugin_cache.xml