Why does the deployment fails due to "java.lang.NoClassDefFoundError: IllegalName" in EAP ?

Issue

• Deployment fails due to the following error:

  ERROR [AbstractKernelController] Error installing to PostClassLoader: name=vfsfile:/jboss-as/server/default/deploy/app-ear/ state=ClassLoader mode=Manual requiredState=PostClassLoader
  org.jboss.deployers.spi.DeploymentException: Error during deploy: vfszip:/C:/jboss-as/server/default/deploy/app-ear/lib.jar/
      at org.jboss.deployers.spi.DeploymentException.rethrowAsDeploymentException(DeploymentException.java:49)
      at org.jboss.deployers.plugins.deployers.DeployerWrapper.deploy(DeployerWrapper.java:185)
  at org.jboss.deployers.plugins.deployers.DeployersImpl.doDeploy(DeployersImpl.java:1454)
  at org.jboss.deployers.plugins.deployers.DeployersImpl.doInstallParentFirst(DeployersImpl.java:1172)
  at org.jboss.deployers.plugins.deployers.DeployersImpl.doInstallParentFirst(DeployersImpl.java:1225)
  at org.jboss.deployers.plugins.deployers.DeployersImpl.install(DeployersImpl.java:1113)
      ...
      at java.lang.Thread.run(Thread.java:662)
  Caused by: java.lang.NoClassDefFoundError: IllegalName: org/lib/package/ClassName
  at java.lang.ClassLoader.preDefineClass(ClassLoader.java:476)
  at java.lang.ClassLoader.defineClassCond(ClassLoader.java:625)
  at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
  at org.jboss.classloader.spi.base.BaseClassLoader.access$200(BaseClassLoader.java:67)