ContributionsMost RecentMost LikesSolutionsRe: Unable to start start after upgrade to 5.6 The version was the latest aka the default. openjdk 11. But the fix is simple - 1. Open a Terminal 2. run Java --version and note your version 3. run sudo update-alternatives --config java 4. select the openjdk 8 and test. You may have to try a couple of versions, depending on the age of your system. Unable to start start after upgrade to 5.6 Running Ubuntu 20.04.2 LTS just downloaded and installed. Can no longer start java.lang.UnsupportedClassVersionError: com/eviware/soapui/SoapUI has been compiled by a more recent version of the Java Runtime (class file version 53.0), this version of the Java Runtime only recognizes class file versions up to 52.0 at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:763) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) at java.net.URLClassLoader.defineClass(URLClassLoader.java:467) at java.net.URLClassLoader.access$100(URLClassLoader.java:73) at java.net.URLClassLoader$1.run(URLClassLoader.java:368) at java.net.URLClassLoader$1.run(URLClassLoader.java:362) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:361) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349) at java.lang.ClassLoader.loadClass(ClassLoader.java:357) at com.exe4j.runtime.LauncherEngine.launch(LauncherEngine.java:81) at com.install4j.runtime.launcher.UnixLauncher.main(UnixLauncher.java:62) Solved