Eclipse NoClassDefFoundError on maps

Eclipse NoClassDefFoundError on maps

I'm trying to run maps and I'm getting the following error. It looks like
I am not declaring something properly. Can anyone help?
08-17 10:50:03.363: E/AndroidRuntime(23422): FATAL EXCEPTION: main
08-17 10:50:03.363: E/AndroidRuntime(23422):
java.lang.NoClassDefFoundError: com.google.android.gms.R$styleable
08-17 10:50:03.363: E/AndroidRuntime(23422): at
com.google.android.gms.maps.GoogleMapOptions.createFromAttributes(Unknown
Source)
08-17 10:50:03.363: E/AndroidRuntime(23422): at
com.google.android.gms.maps.SupportMapFragment.onInflate(Unknown Source)
08-17 10:50:03.363: E/AndroidRuntime(23422): at
android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:271)
08-17 10:50:03.363: E/AndroidRuntime(23422): at
android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:669)