Just wanted to share for others to know how to resolve this issue.
I am trying to launch Soap UI OS, but I get this error.
I even restarted my computer and I still get this error.
I update my Java from 8u201 to 8u211.
I looked deeper.
I was launching SOAP UI via the Start Menu.
This was invoking SOAP UI v5.4 instead.
I saw that my Program Files had both v5.4 and v5.5 so I deleted v5.4
java.lang.NoClassDefFoundError: org/apache/commons/cli/CommandLineParser at java.lang.Class.getDeclaredMethods0(Native Method) at java.lang.Class.privateGetDeclaredMethods(Unknown Source) at java.lang.Class.getDeclaredMethod(Unknown Source) at com.exe4j.runtime.LauncherEngine.launch(LauncherEngine.java:83) at com.exe4j.runtime.WinLauncher.main(WinLauncher.java:94) at com.install4j.runtime.launcher.WinLauncher.main(WinLauncher.java:25) Caused by: java.lang.ClassNotFoundException: org.apache.commons.cli.CommandLineParser at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) ... 6 more