MediaRecorder start is been failing

Question

I am trying to record the call when phone call is accepted in android.

For that I have created a Receiver, in that I have kept code for MediaRecorder initial setup like this..

onReceive(){

    recorder = new MediaRecorder();
    outputFile = Environment.getExternalStorageDirectory().
                      getAbsolutePath() + "/myrecording"+System.currentTimeMillis()+".3gp";

    recorder.setAudioSource(MediaRecorder.AudioSource.VOICE_CALL);
    recorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
    recorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB); 
    recorder.setOutputFile(outputFile);

 }

and in the phoneState change listener, for the case OFF_HOOK

case TelephonyManager.CALL_STATE_OFFHOOK: {
    Log.v(TAG,"call state is OffHook");
    try{
        recorder.prepare();
        Thread.sleep(1000);
        recorder.start();

    } catch(Exception e) {
        Log.e(TAG,"Error occured here");
    }
    break;
}

every time when the control comes into this state I am getting error saying that

E/MediaRecorder(23056): start failed: -2147483648
W/System.err(23056): java.lang.RuntimeException: start failed.

I tried this but it is also not working, could you please help me in this.Thanks