If, like me, you’ve been putting this exception off because it only happens once in every few startups, well don’t, because it’s a simple fix! For me, I get it just after the INFO: Starting Coyote HTTP/1.1 on http-8088 lines in my Tomcat v5.0.x (Windows) log. The problem is highlighted in this bug report, and the fix is simply to:

• Download “JMX 1.2.1 Reference Implementation” from the Sun Download page.
• Shutdown Tomcat
• Delete the existing $TOMCAT_HOME/bin/jmx.jar
• Extract lib/jmxri.jar, from the zip, and put it in your $TOMCAT_HOME/bin directory, renaming it jmx.jar
• Restart Tomcat, and have one less problem!

$TOMCAT_HOME, is your Tomcat intsallation directory (the folder that contains the folders bin, common, conf, etc.).