Sliding Menu NoClassDefFoundError

Sliding Menu NoClassDefFoundError

I am using SlidingMenu (https://github.com/jfeinstein10/SlidingMenu) and
below is my code:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
SlidingMenu menu = new SlidingMenu(this);
menu.setMode(SlidingMenu.LEFT);
menu.setTouchModeAbove(SlidingMenu.TOUCHMODE_FULLSCREEN);
menu.setShadowDrawable(R.drawable.shadow);
menu.setFadeDegree(0.35f);
menu.attachToActivity(this, SlidingMenu.SLIDING_CONTENT);
menu.setMenu(R.menu.main);
}
but whenever I run my app, I get the following error:
E/AndroidRuntime(30206): java.lang.NoClassDefFoundError:
com.jeremyfeinstein.slidingmenu.lib.SlidingMenu
The sliding menu project has been marked as Library (IsLibrary = checked)
and I went to my project properties -> java build path -> projects and
added the project, but still it is not working.
Any help would be very much appriciated