Problems with playing AAC Raw data on Silverlight (Windows Phone)

Question

I need to play AAC LC audio that comes from live stream. To achive that i've implemented MediaStreamSource.

When i receive first packets of stream, i set MediaElement's source to my MediaStreamSource. It seems that everything works fine: OpenMediaAsync is called -> reported with ReportOpenMediaCompleted, then GetSampleAsync is called -> reported with ReportGetSampleCompleted, BUT, on 10th call of GetSampleAsync, ReportGetSampleCompleted is throws NullReferenceException.

Here is my CodecPrivateData:

var waveFormat = new AACWaveFormat();
waveFormat.FormatTag = 0xFF;
waveFormat.Channels = 2; // For my stream is always stereo
waveFormat.Frequency = 44100; //For my stream is always 44Khz
waveFormat.BitsPerSample = 16;  //For my stream is always 16bit
waveFormat.BlockAlign = waveFormat.Channels * waveFormat.BitsPerSample / 8; //is this true formula?
waveFormat.AverageBytesPerSecond = waveFormat.Frequency * waveFormat.BlockAlign; //is this true formula?  because usually this value is 176400 or 1411Kbps is this real value for sound?
waveFormat.ExtraDataSize = 2; //usually, but i read these values from first packet of stream
waveFormat.ExtraData = AudioSpecificConfig; //AudioSpecificConfig usually 2 bytes length, readed from stream.

First packet of the stream is always AACSequenceHeader - where i read my CodecPrivateData and AudioSpecificConfig. All the rest is AACRaw.

My CodecPrivateData is looks like FF00020044AC000010B102000400100002001210.

My GetSampleAsync

protected override void GetSampleAsync(MediaStreamType mediaStreamType)
{
    var audioStreamDescription = new MediaStreamDescription(MediaStreamType.Audio, AudioStreamAttibutes);  //AudioStreamAttibutes is field that contains data filled on OpenMediaAsync step.
    //using (var memoryStream = new MemoryStream(AudioPackets[0].Data))
    var memoryStream = new MemoryStream(AudioPackets[0].Data);
    ReportGetSampleCompleted(new MediaStreamSample(audioStreamDescription, memoryStream, 0, AudioPackets[0].Data.Length, TimeSpan.FromMilliseconds(GetAudioSampleCalls++ * 32).Ticks, new Dictionary<MediaSampleAttributeKeys, String>()));  //throws NullReferenceException, when debugger stops i can be see that all passed params is not null!
}

The problem here is that i don't know any timestamp and i don't know whether this could be a problem.

And finally what is Data field? Data field contains all received RawAAC audio as Byte[] that i extract from AudioTag. (See E.4.2.2 AACAUDIODATA at http://download.macromedia.com/f4v/video_file_format_spec_v10_1.pdf)