Under Java 1.7_u51 security has been beefed up, so it now refuses to start Chainsaw 2.0alpha-1. The Exception tab of the details window shows: java.lang.SecurityException: Missing required Permissions manifest attribute in main jar: http://logging.apache.org/chainsaw/webstart/lib/log4j-chainsaw-2.0alpha-1.jar at com.sun.deploy.security.DeployManifestChecker.verifyMainJar(Unknown Source) at com.sun.deploy.security.DeployManifestChecker.verifyMainJar(Unknown Source) at com.sun.javaws.Launcher.doLaunchApp(Unknown Source) at com.sun.javaws.Launcher.run(Unknown Source) at java.lang.Thread.run(Unknown Source)