After upgrading to Jenkins version 1.568 it can not start.
The following is the last entry in the log file no matter how long I wait.

Exception in thread "Thread-3" java.lang.ClassCircularityError: java/util/logging/LogRecord
at net.bull.javamelody.LoggingHandler.publish(LoggingHandler.java:109)
at java.util.logging.Logger.log(Logger.java:616)
at java.util.logging.Logger.doLog(Logger.java:641)
at java.util.logging.Logger.log(Logger.java:730)
at winstone.Logger.logInternal(Logger.java:157)
at winstone.Logger.log(Logger.java:165)

Stopping Jenkins again and deleting file ./plugins/monitoring.jpi and folder ./plugins/monitoring/ allows me to get Jenkins running again, so that can work as a workaround