why is tapjoy not working?

HI, recently I downloaded the Tapjoy (unity3d) sdk I read the documentation on the tapjoy website and i followed the steps. I created a new empty project i imported the package and i started the sample scene. My Problem is : when I try to build my project there's an error in the TapjoyPluginAndroid,css file "Exception: JNI: Init'd AndroidJavaClass with null ptr!" and the ads wont show up on my phone. Please help me .