Android error - class not found

After I successfully developing and testing my app on iOS, I now moved to the Android sim, but am getting class not found errors. How can I fix the dependencies? I have deleted and re-added the platform/android folder many times…

D/PluginManager( 1542): init()
W/System.err( 1542): java.lang.ClassNotFoundException: org.apache.cordova.device.Device
W/System.err( 1542): 	at java.lang.Class.classForName(Native Method)