after you edit jrun configuration from http://localhost:8000 or services jrun admin/cfusion can not start from anywhere (service mmc/jrun launcher). this issue is mainly related to java/jre home. if you are not updated with Jrun4 with updater7 than you can not use jre 1.5 or higher. to start jrun again edit file jvm.config (c:\jrun4\bin) and edit java.home line and make sure to use jre/jdk 1.4. also edit system variable JAVA_HOME to old version.
You can also update Jrun4 with updater7 to resolve this issue. after update you can use Java 1.5 and above.