I'm trying to run the desktop version of my LibGDX project, but getting following error ..

Exception in thread "LWJGL Application" com.badlogic.gdx.utils.SerializationException: Error reading file: ui/uiskin.json at com.badlogic.gdx.scenes.scene2d.ui.Skin.load(Skin.java:97) at com.badlogic.gdx.scenes.scene2d.ui.Skin.<init>(Skin.java:74) at com.mygdx.game.MainMenu.show(MainMenu.java:51) at com.badlogic.gdx.Game.setScreen(Game.java:61) at com.mygdx.game.Splash$1.run(Splash.java:48) at com.badlogic.gdx.scenes.scene2d.actions.RunnableAction.run(RunnableAction.java:42) at com.badlogic.gdx.scenes.scene2d.actions.RunnableAction.act(RunnableAction.java:32) at com.badlogic.gdx.scenes.scene2d.actions.SequenceAction.act(SequenceAction.java:65) at com.badlogic.gdx.scenes.scene2d.Actor.act(Actor.java:95) at com.badlogic.gdx.scenes.scene2d.Group.act(Group.java:49) at com.badlogic.gdx.scenes.scene2d.Stage.act(Stage.java:223) at com.badlogic.gdx.scenes.scene2d.Stage.act(Stage.java:186) at com.mygdx.game.Splash.render(Splash.java:29) at com.badlogic.gdx.Game.render(Game.java:46) at com.mygdx.game.ColorCatch.render(ColorCatch.java:19) at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:215) at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:120) Caused by: com.badlogic.gdx.utils.SerializationException: Error reading file: ui/uiskin.json at com.badlogic.gdx.utils.Json.fromJson(Json.java:683) at com.badlogic.gdx.scenes.scene2d.ui.Skin.load(Skin.java:95) ... 16 more Caused by: com.badlogic.gdx.utils.SerializationException: at com.badlogic.gdx.scenes.scene2d.ui.Skin$2.read(Skin.java:416) at com.badlogic.gdx.scenes.scene2d.ui.Skin$2.read(Skin.java:410) at com.badlogic.gdx.utils.Json.readValue(Json.java:867) at com.badlogic.gdx.scenes.scene2d.ui.Skin$1.readValue(Skin.java:404) at com.badlogic.gdx.utils.Json.fromJson(Json.java:681) ... 17 more Caused by: com.badlogic.gdx.utils.reflect.ReflectionException: Class not found: com.badlogic.gdx.scenes.scene2d.ui.Tooltip$TooltipStyle at com.badlogic.gdx.utils.reflect.ClassReflection.forName(ClassReflection.java:30) at com.badlogic.gdx.scenes.scene2d.ui.Skin$2.read(Skin.java:414) ... 21 more Caused by: java.lang.ClassNotFoundException: com.badlogic.gdx.scenes.scene2d.ui.Tooltip$TooltipStyle at java.net.URLClassLoader$1.run(URLClassLoader.java:366) at java.net.URLClassLoader$1.run(URLClassLoader.java:355) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:354) at java.lang.ClassLoader.loadClass(ClassLoader.java:425) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308) at java.lang.ClassLoader.loadClass(ClassLoader.java:358) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:191) at com.badlogic.gdx.utils.reflect.ClassReflection.forName(ClassReflection.java:28)

Project structure is the following ..

rob@work:~/git/test$ ls android core gradle gradlew ios local.properties build.gradle desktop gradle.properties gradlew.bat libs settings.gradle rob@work:~/git/test$ ls android/assets/ui/ default.fnt uiskin.atlas uiskin.json uiskin.png

Simplified version of MainMenu ..