libGdx error

Im trying to make a game with libGdx and im getting this error
Exception in thread “main” java.lang.NoClassDefFoundError: com/badlogic/gdx/jnigen/NativeCodeGenerator
at com.badlogic.gdx.utils.GdxBuild.main(GdxBuild.java:55)
Caused by: java.lang.ClassNotFoundException: com.badlogic.gdx.jnigen.NativeCodeGenerator
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
… 1 more

What is causing this?