Zembra Xamarin EMDK ScannerException

Hi.

I am tring this code: http://techdocs.zebra.com/emdk-for-xamarin/3-0/tutorial/barcodeapitutorial/

Basic Scanning Tutorial using Barcode API - Zebra Technologies Techdocs

It seems to work but I have an exception here:

   try
  
{

  
//Get the feature object such as BarcodeManager object for accessing the feature.
  barcodeManager
= (BarcodeManager)emdkManager.GetInstance(EMDKManager.FEATURE_TYPE.Barcode);

  scanner
= barcodeManager.GetDevice(BarcodeManager.DeviceIdentifier.Default);

  
if (scanner != null)
  
{

  
//Attahch the Data Event handler to get the data callbacks.
  scanner
.Data += scanner_Data;

  
//Attach Scanner Status Event to get the status callbacks.
  scanner
.Status += scanner_Status;

  scanner
.Enable();

  
//EMDK: Configure the scanner settings
  
ScannerConfig config = scanner.GetConfig();
  config
.SkipOnUnsupported = ScannerConfig.SkipOnUnSupported.None;
  config
.ScanParams.DecodeLEDFeedback = true;
  config
.ReaderParams.ReaderSpecific.ImagerSpecific.PickList = ScannerConfig.PickList.Enabled;
  config
.DecoderParams.Code39.Enabled = true;
  config
.DecoderParams.Code128.Enabled = false;
  scanner
.SetConfig(config);

  
}
  
else
  
{
  displayStatus
("Failed to enable scanner.\n");
  
}
  
}
  
catch (ScannerException e)
  
{
  displayStatus
("Error: " + e.Message);
  
}

When the execution reach scanner.SetConfig, I receive an exception:

Already scanning. Wait for current scanning to complete

I don't understand which could be the problem, but in this way the configuration is not accepted.

Thanks

Alessandro