android wear - audio capture failure

I was using the sample codes in http://ift.tt/1IiXn1x to capture the audio on the android wear. It works good on my handheld, but does not work on my smart watch. The error is: java.lang.RuntimeException: start failed The error happened in mRecorder.start(), see code segment below:

private void startRecording() {
    mRecorder = new MediaRecorder();
    mRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
    mRecorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
    mRecorder.setOutputFile(mFileName);
    mRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);

    try {
        mRecorder.prepare();
    } catch (IOException e) {
    Log.e(LOG_TAG, "prepare() failed");
    }
    mRecorder.start(); // error
}

What do I need to do? Thanks