AudioClip:GetData invalid parameter

I'm trying to obtain a real time audio feedback on a microphone. The code above is working but after a while I'm having the following error :

I didn't find much about those errors, any idea ?

Code (CSharp):

1.  
2.   public void restart()
3.   {
4.     microphone_name = DEFAULT_DEVICE_NAME;
5.  
6.     int i = 0;
7.     foreach(var d in Microphone.devices)
8.     {
9.       if(i++ == microphone_index)
10.       {
11.         microphone_name = d;
12.  
13.       }
14.     }
15.     audio.clip = Microphone.Start(microphone_name, false, 100, 44100);
16.     audio.Play();
17.     play();
18.   }
19.  
20.  
21.   void Update ()
22.   {
23.     int newOffset = Microphone.GetPosition(microphone_name);
24.       int nbSamplesToRetrieve;
25.       if (newOffset < sampleOffset)
26.           nbSamplesToRetrieve = newOffset + audio.clip.samples - sampleOffset;
27.       else
28.           nbSamplesToRetrieve = newOffset - sampleOffset;
29.       float[] samples = new float[nbSamplesToRetrieve];
30.       float sampleRate = audio.clip.frequency;
31.  
32.     audio.clip.GetData(samples, sampleOffset);
33.  
34.       var pitch = autoCorrelate( samples, sampleRate );
35.  
36.        if (pitch != NOT_ENOUGH_DATA)
37.        {
38.           sampleOffset = newOffset;
39.            if (pitch >= 0)
40.            {
41.                //detected a pitch
42.                currentPitch = pitch;
43.            }
44.            else
45.            {
46.                //did not detect anything
47.                currentPitch = -1;
48.            }
49.       }
50.   }

 

Any solutions for this?