From your code, since repTimer.isPlaying() is getting invoked, I assume that the JAVA repTimer object is not NULL. However, IllegalStateException is triggered when the native MediaPlayer object is NULL (Reference: http://androidxref.com/4.2.2_r1/xref/frameworks/base/media/jni/android_media_MediaPlayer.cpp#380 ). Hence, there is some mismatch between your JAVA states and native states.
P.S: You may want to check the code prior the position pasted in this question. In some earlier method call, the native object has been destroyed which is not reflected in your JAVA object state.